I was alone at last, although the noises of the Base still hummed and sputtered in my ears. I switched off the light and groped my way to the neoglass window. As my eyes adjusted, details emerged into the spectral clarity of the months-long night. Unsoftened by any wisp of atmosphere, the stark and frigid landscape gleamed sullenly beneath a sky jangling with stars as sharp and hard as drilling-bits. A strange chill crawled along my nerves, excitement spiked with fear. Here was I, gazing upon the nightside of Mercury, the inmost and smallest of the solar planets: a brutally hostile, deadly little world sweeping an eccentric orbit around a monstrous sun.

The door behind me opened. A click, and the room exploded into light. I blinked, blinded; then turned.

"You must be Dr. Collins—Christopher Collins?" said the gray-uniformed, prematurely gray-haired stranger who filled the doorway.

"Yes," I replied.

He moved forward, light-footed for his bulk. Without ceremony he introduced himself: Commander Peter Craig, United European Space Service, Mercury Base Three. He was in command of the two-pronged project nicknamed "The Hot Spot Expedition." One prong was purely scientific: to investigate the nature of subsolar volcanism during perihelion passage. The other was more immediately practical: to confirm the existence of rich deposits of uranium in the hot' spot regions, and to pinpoint their positions so that the precious element could be extracted by night-side teams and shipped to our uranium-hungry Earth.

Craig chuckled. "One thing we're indebted to you for: the stink you kicked up when you learned of our obsolete equipment! Thanks to you, we've at last been given what we need to bounce Mercury back into the limelight where it belongs."

"I'm glad," I said, and meant it. Mercury Bases One and Two had been closed down long ago, and Base Three starved of funds for years.

Craig fell silent, then: "This is not your first trip off Earth," he stated.

"No," I agreed. "I've worked on Saturn's moon, Iapetus, and in the seismically active regions of Mars."

"Titan? Weren't you there with the Heilbron Expedition last year?"

"No. I couldn't make it."

"Why not?"

"Broke my leg."

"How?"

"Slipped on the ice on Erebus."

Craig laughed. "Teach you to go scrambling around on Antarctic volcanoes!"

"A geologist goes where he's sent, on Earth or off it," I retorted. I had a guilt complex about that leg. I'd broken it through staying too long in an unstable zone, poking instruments down smoking fumaroles; I'd had to bolt for cover.

Craig turned to the window. The vivid blue eyes set deep in his glare-bronzed face narrowed as he scanned the darkness outside. His size made me uncomfortable. I'm a small man, wiry and agile, with sandy hair and eyes to match. Beside this giant I felt microscopic.

Craig said idly, "When I came in, you were standing here with the light off. Does Mercury impress you?"

"Very much," I answered truthfully. Some quirk of temperament ensures that the more I travel the keener grows my zeal to explore strange places and unravel new mysteries.

With shocking abruptness Craig's manner changed. "That's what I feared," he said. "Dr. Collins, I know your reputation. You're damned good at your job—you wouldn't be here if you weren't!—but you take hair-raising risks. So far you've got away alive though not always intact." His voice became velvet over a razor blade. "Here you will behave more sensibly. Mercury is a killer planet. One act of folly on your part, and you'll throw away men's lives and equipment worth millions. Men can be replaced, including you. The equipment is irreplaceable. There will be no heroics. Do I make myself clear?"

He did. I could not tell him so; the unexpectedness of his attack had stolen the air from my lungs. I felt my face grow pale with shock and rage. No one had spoken to me like this in years.

As for his earlier questions, so innocent, so friendly, how I had been deceived! Craig had asked them, not to toss a social hand-line, but to provide a launching pad for his savage little homily.

Craig gave a sudden boyish grin and slapped me lightly on the arm. "Enough. Time to visit the daysider, check your gear, meet the crew. But first, may I give you a final word of advice?"

Hoarsely I forced out: "If you must."

"Stop gaping at me as though I'd sprouted horns and a tail!"

Seconds later Craig was striding to the door. I struggled to arrange my expression to show bright good humor, and hurried after him.

The crew of two was already aboard the daysider, an exploration vehicle designed to operate in full sunlight. Safe in its shielded entrails, I would be borne to the hot spot tomorrow, Earth-time.

Inside the air lock, Craig helped me off with my borrowed spacesuit. I tested my legs and noted with relief that the gravity generator was switched on and I was my own natural Earth-weight. I breathed air redolent of oil and warm metal. I listened to the two voices dropping clearly from the intercom, which someone had left open ... one voice, to be exact: a monologue punctuated by the hearer's ribald guffaws.

"So I said to her, 'Look, pussycat, six times in two hours is more than enough. I need to recharge my batteries. I want to sleep. Move over.'"

These bedtime antics were related in an English too impeccable to be the speaker's native tongue. The storyteller must be our navigator, Giovanni Ricci: one of the Italians among the multilingual Mercury Base personnel.

"Alas," continued Ricci with an elaborate sigh, "she refused to budge. She wanted to cuddle me, she said. 'But,' I protested, 'you're wrapped around me like an octopus. That's not cuddling. That's sheer bad manners.' She replied that she was demonstrating her undying love. I was flattered—until the truth dawned: she wasn't cuddling me because she loved me but because she was cold." Ricci's light attractive voice throbbed with indignation. "Know what she said then? 'Swap sides with me, carissimo. I'll warm your half. You warm mine.' The cheek of it! My half was warm already. Hers was freezing. I refused, of course. I rolled over, wedged my bottom against her tummy and shoved."

"And did it work?" That was presumably our engineer, Mark Anderson. He was spluttering with mirth.

"Alas, no. We were both in her half all along. My shove gave birth to the most frightful commotion. I'd heaved her onto the floor."

Having stowed our spacesuits, Craig led me along the passage from the air lock to the control cabin which filled the daysider's forward end. Ricci and Anderson sprang to their feet as we entered. Craig introduced them. Young men, both: Ricci, dark and lithe, with a sallow fine-boned face and eyes so deep a brown that they looked, in the artificial light, like pools of pitch; and Anderson, built like a boxer, stolid and square, with a fuzz of fair hair matting his wrists and curling from the V of his uniform collar.

"To work," said Craig briskly.

Suppressing a surge of excitement (I love my job), I set about preparations. They should have been simple: to check the equipment installed for my use. There was just one snag: space—or rather the lack of it. How severe that lack was would soon become dismayingly clear.

"No, Dr. Collins, I'm sorry, but you can't," said Craig, seating himself in the pilot's chair and eyeing my contortions with misgiving.

"Can't what?" I asked.

"Park your gear so close to the window. It's blocking my view. I'm piloting this sardine can, remember."

I stopped short. It was true: my bulky instruments were festooning the heavily reinforced neoglass window which gave forward vision to pilot and copilot—except that on this trip we would carry no copilot. I would he using his chair; no other arrangement was workable.

I reshuffled my apparatus: large items to the wall, small items to the front where I would have them comfortably to hand . . .

"Sorry, Doctor. No. I've got to be able to reach the controls. I can't if all the time I'm bashing my fingers on some gadget of yours that's in the way."

I scowled at the control board stretching the length of the wall below the window. I moved my instruments again.

"Whoa, Doctor! Stop! That's Ricci's table. Tomorrow it's going to be covered with navigation charts."

I glared at the table almost touching the backs of our chairs, and exploded. "All right, Commander, you tell me how the hell I'm supposed to manage if I can't have my gear anywhere within my reach."

"Stow it beside your chair—"

"I can't. There's no room."

"Of course there isn't! The daysider wasn't designed to hold all this newfangled equipment. Make room as best you can."

"How?" My voice rose half an octave. My hands waved wildly at the instruments cluttered around me, each bristling with sharp projections and snakes' nests of cables looping to the wall. "If I leave my stuff where it is, I'll be zipping about like a squirrel in a net. I'll bruise myself black and blue. I'll strangle myself in all those bloody cables—"

Craig's voice boomed out, drowning mine: "Too had, Doctor, but you'll have to cope. Somehow. So will the rest of us."

Silence descended, breached by muffled merriment from Ricci and Anderson—merriment which fizzled out under a single stern glance from Craig, who brooked no insubordination.

Eventually my apparatus was checked and arranged as conveniently as the cramped space allowed. I sagged wearily into the copilot's chair. Craig produced a flask of hot coffee. Politely he offered me some. Politely I accepted, reaching to receive a large mug filled to the brim.

"There are four exploration vehicles, are there not—two daysiders and two nightsiders?" I hoped a light remark might thaw the chilly courtesy which threatened to asphyxiate us.

A frisson rippled through the cabin. My companions were momentarily as still as stalagmites. The frisson passed. Craig said easily, "There used to be. One daysider went missing. Didn't you read about it in the papers on Earth?"

Of course I did, I recalled too late, and cursed my thoughtless blunder. I buried my embarrassment in my coffee, gulping so deeply that I scalded my mouth. I mumbled, "I believe I may—"

"This was two perihelions ago," Craig cut in, perhaps to sidestep further awkwardness. "Our sister craft set out to make a hot spot crossing. She never returned."

"What happened to her?"

"No idea."

"You must have some theory, surely?"

"None, Dr. Collins. I headed the search for her myself, in this craft. We found no trace. But"—Craig's gaze locked on mine, grim and very clear—"she had a competent and careful crew. Whatever happened, those men died through no fault of their own."

You take hair-raising risks. There will be no heroics. I stiffened. If Craig dared to tongue-lash_, me with Ricci and Anderson lapping up every word . . .

"You're spilling your coffee," warned Craig.

I righted my tipping mug, and swore at the brown stain spreading along the hem of my clean white overall. To have been harangued as though I were a naughty child—and for nothing! I never take risks. Well, only when forced to by the nature of my work.

Lifted by gravity-neutralizing motors safely above the fissured ground, the daysider whined through the night. A fan of light illuminated the route ahead. Beyond the fan a lake of radioactive dust flared into sickly fluorescence, then faded. A mineral outcrop crept into a corner of the fan and burst into prismatic sparks. The terrain spoke of immeasurable age battered by extremes of temperature, alternately frozen and superheated as Mercury turned its airless face slowly, very slowly, from the bitter cold of the nightside to the blowtorch glare of the sun.

The Hot Spot Expedition was under way.

I sat quietly in the copilot's seat. Craig filled the chair beside me, his powerful hands riding the controls with casual ease. Behind us Ricci rustled navigation charts, his cleanly chiseled face relaxed yet alert under its cap of sleek black hair. Anderson was absent; he was supervising the engines tucked away in a compartment beyond the washroom, to the rear.

Craig broke the silence. "Dr. Collins, we shall be flying on instruments only for the next half hour."

"Why?" I asked.

"We're approaching the terminator—the dividing line between day and night. In a few minutes the sun will appear on the horizon ahead. We'll be flying straight toward it."

I tensed. With straining eyes I probed the darkness in front of us. Darkness? A cone of pearly luminescence stabbed up from below the horizon. Lengthening rapidly, it arrowed into the sky. I had seen it from Mars, this zodiacal light, but never so magnificently. So brightly it glowed that the ground itself reflected a pallid shine.

Moments later a brilliant haze limned the ragged skyline. It arched upward, spread, intensified. "The sun's corona," Craig told me. "The sun itself will follow." He pressed a button. A glittering shutter of heat-shield material sank silently over the outside of the window, chopping off the view. It would stay lowered until the sun had lifted high enough to be above our line of sight.

Craig studied the control board, concentrating on a small color-television screen inset among the dials and switches. I eased forward and saw why: the screen gave a view to the front. I examined it . . . and felt the breath lock in my throat. A blazing bow had reared beneath the arch of the corona, dimming it to a ghost. The body of the sun was rising. More and more of it kept coming; it seemed to have no end. Sluggishly it heaved itself into the sky, annihilating the last few faded stars.

Details from my briefing lunged to the forefront of my mind. Mercury was now at perihelion, that point along its lopsided orbit where it whipped in closest to the sun. For many Earth-weeks past the sun had been growing larger and larger as it crawled up the sky. It was hovering now at the zenith, swollen to its most immense size. Hovering? Like a fiery pendulum it had reversed its motion and swung backward for a fortnight before resuming its forward path.

Under that thrice-crossed zenith lay the hot spot toward which we were traveling with such crazy confidence.

The hot spot: one of the two which Mercury bore on opposite sides of its equator. At alternate perihelions, each crept vertically under the sun and shuddered into volcanism—volcanism which crescendoed to planet-bursting violence during the period of greatest heat.

With a hideous shock the full realization punched home: this was the period of greatest heat; I was racing to the hot spot; I would soon be pinned between that gigantic fireball and the flaming cauldron of the land . . . with no shelter, no shadow to creep under for safety.

Safety? One daysider had been lost already, two perihelions ago—lost, therefore, in the region I was to study; lost without trace. In other words, rendered unrecognizable by the manner of its destruction.

The cabin seemed suddenly like the inside of a runaway nuclear reactor. As inconspicuously as possible I eased my collar from my throat, then rubbed my hands down my overall.

"Cheer up," said Ricci behind me.

I started convulsively; turned.

"It catches all of us like that the first time out," Ricci explained, and flashed me a wicked grin. "Er—your elbow is about to poke the glass out of one of your gadgets."

So it was. I jerked back my arm, appalled at the prospect of damaging my precious equipment.

Craig pressed a button and the segment of heat-shield covering the window rose. I looked out on a furnace landscape, parched and crumbled. Shadows sprawled across it like accidents with ink.

In quick succession Ricci gave out several course corrections. Craig followed them, then thrust a lever hard down to the floor. Mercury began to glide more swiftly beneath us. The shadows grew shorter, the stonescape still more flayed and, agonized. Like madmen seeking the most frightful stage for suicide, we hurtled toward the hot spot which lay impaled under the vertical blast of the flamethrower.

"Prepare yourself, Dr. Collins." Craig's prosaic voice helped me to shake loose from a state of uncomfortable tension. "Shortly we shall enter the volcanic zone."

I bounded from my seat. With hands that trembled slightly I prepared my instruments for action. The polished coolness of their planes and edges comforted me. I slid my fingers over them with almost sensual affection. Cameras, recording equipment, spectroscope, gauges and meters of various kinds, monocular: all would soon yield sweetly to my will.

Sometimes I have an uneasy suspicion that I prefer things to people.

There was no definite boundary to the hot spot region. Suddenly and unmistakably we were over it. I set the cameras whirring and leaped for the spectroscope, bruising my knee on the corner of my chair. "Slow down!" I cried in anguish. "All I'm getting is a blur!"

Craig said reasonably, "I thought you wanted to make a systematic scan, starting from the center."

"I do, but don't let's rush it. A slow approach will give me a chance to get the feel of the place before I begin."

We slowed down.

The volcano-scape flared all around us. I squeezed past my apparatus and glued my nose to the window, backing off smartly when I found that it was hot. Warily I edged forward again, trying to examine the details outside. The neoglass was darkened and polarized. Even so, a sizzling, upward-striking light slammed into my eyes: the reflected radiance of the vertical, perihelion sun.

Craig's voice roused me. "Dr. Collins! Dr. Collins!"

"Yes?" I said absently.

"It's unwise to stand so close to the window. The glare can hurt your eyes."

I stiffened into full attention. "But I'll need to be close to it from time to time. That's part of my job."

Craig opened a locker in the wall beside him. He groped within, produced a pair of dark glasses. "Wear these," he said. "And keep back from that window as much as you can!"

I perched the glasses on my nose—a button nose with a dent where the bridge should be. Again I studied the outside. The lenses cut down its intolerable brilliancy.

I moved to the tectonic strain gauge, an instrument designed to measure strain in both surface and subsurface rocks without physical contact with either. I stooped to read its dials. The glasses slithered down. I shoved them back, smearing one lens with an impatient finger. The dials were meaningless shadows, their needles darkened to invisibility. I whipped off the glasses and tried afresh. This time the needles stood out clear—and quivering. Their agitation warned of tremendous stresses striving to rip the crust asunder.

Impressed by the magnitude of the forces at work, I turned once more to the window and peered out, frowning in concentration. I found myself chewing the earpiece of the glasses. Guiltily I slipped them on again. Both lenses now were smeared.

We were skirting a cluster of volcanic cones. Ash-gray, leaning at impossible angles, they reared from a floor which blazed white and pale orange hundreds of feet below. Above them boiled thick gritty clouds whose undersurfaces smoldered redly with the reflected glare. Constituent particles soared and plummeted in the low-gravity vacuum. The clouds staged a nightmare spectacle of fiery towers writhing between the tar-black sky and the incandescent ground.

"May we fly between them?" I asked. "I'd like a trial run to make sure that no unforeseen snags emerge."

Craig's cheek muscles twitched. He seemed on the point of refusing, then: "Very well," he said.

Cautiously, very cautiously, we threaded between the cones. I put my instruments through their paces. They functioned splendidly. Gripped by excitement, I called to Ricci, "Got the position logged?"

"But of course," the cheeky devil answered. "Er—you're shedding those goggles again."

True. The wretched things had skidded down my nose like toboggans down an ice run. Swearing, I rescued them.

"Getting the feel of things, Dr. Collins?" Craig inquired. He sounded amused.

I halted abruptly. I had almost forgotten that Craig was our pilot. I had been flitting around him, buffeting him with my apparatus, breathing heavily in his ear. "Thank you, yes," I replied, ruefully aware of error. One snag did exist: my own excitability. In future I must remember to flit with care.

A nearby cone blew itself silently to fragments. Craig yanked levers. The daysider skipped nimbly out of the danger zone.

"Jesus," I murmured when my voice returned. "Does that happen often?"

"We don't know," said Craig. "One needs to be perpetually on guard."

Ricci added slyly, "One needs also very much not to have a nervous disposition!"

A muscle bunched in the corner of my jaw. Some people think, quite wrongly, that I have a nervous disposition. I realized that I didn't like Ricci, not at all. He was too knowing, too insolent.

I must be honest: my dislike stemmed from a core of plain old-fashioned jealousy. I resented Ricci's Latin good looks and air of sexual assurance. I recalled the bedroom adventure which he had described with such hilarity. I would have liked to chalk up similar exploits. I would have liked to tell naughty tales of my virility. I would have liked to be a wow with the ladies.

Pipe dreams. I've always muffed my contacts with women. I'm sensitive about my smallness. I can't dance. My attempts at cocktail party chat undergo a sea change into lectures on geology. I watch female interest fade as, helpless, I wax more and more abstruse. Female eyes glaze with boredom. Surreptitiously but with mounting desperation they search for a rescuer. A rescuer invariably appears, and my latest conquest wafts away with insincere murmurs of regret.

Mercury rolled below, convulsed. Despite the dark glasses, my eyes itched and stung as I scanned that riot of lethal light. I rubbed them fiercely and carried on, determined not to let physical weakness interfere with my enthralling work.

Twice Craig warned me away from the window.

I was adjusting to Mercury's bizarre violence, although I was no closer to explaining it away. Eons ago, this vicious little world should have quenched the last of its volcanoes. The question niggled like a sore tooth: why had it not?

Regretfully I thrust speculation aside. The time had come to begin the systematic scan. Craig nodded when I told him. Ricci looked up with a sardonic glint which plainly stated, High time too!

The daysider sped the rest of the way to the hot spot's center. Ricci's most exacting task now began. As navigator, he was to guide us out in a pattern of expanding squares which would cover every yard of the terrain.

The daysider floated forward, its path making right-angle turns frequently at first, then less and less often. I set my instruments to make broad slow sweeps across the searing white and yellow expanse. Here and there darker features glowed in all shades of red from cherry to charred crimson-black. Their outlines were indistinct, for they cast no shadows under the pounding radiance of the vertical sun.

I examined the terrain. I studied the printouts from the recorders. I took readings from my instruments.

I marked the sites of radioactive ores. Gradually, gradually, the dim outlines of a chaotic picture began to emerge. Sharp discontinuities and fluidic mergings: they were not arranged in an orderly manner; they were jumbled higgledly-piggledy as though a giant spoon had dug deep into the crust and stirred with stupendous strength.

Three hours slipped past. We glided over a region of overlapping craters. I swung the monocular into position—a useful gadget, like a short-range telescope on a jointed stalk. I adjusted its focus, increased its magnification, squinted into it painfully. Long since I had abandoned my dark glasses. Their lenses were a mess of smudges. Cleaning them was useless; each time I put them on, they steamed up within seconds.

Grotesquely magnified by the monocular, the craters wavered in the heat-glare. They looked wrong somehow. I bent over my instruments. Their readings indicated an increase in gravitational pull over this region. The direction of pull was measurably out of alignment with the gravitational field of the planet as a whole. A mascon lay hidden underground—a mascon fizzing with hard radiation. Uranium! The mascon was riddled with the stuff, begging to be mined and ferried to power-starved Earth.

Enough. I needed no more at present. Detailed analysis must await my return to Europe.

I straightened and kneaded the small of my aching back. I frowned through the window, studying the patchwork of ruined craters. An obscure pattern seemed to underlie their subtle wrongness. Could this entire zone, mascon and all, be one monstrously huge, inactive caldera?

Inactive? On Mercury, near the center of a hot spot, at perihelion?

I made a dive for the strain gauge, read its message frantically. And read it again, unable to believe my eyes: the needles were like live things demented with terror, striving to burst from their confinement and go whirling off the ends of their scales.

Before I had time to yell a warning, Craig sent the daysider shrieking upward into the ebony sky.

Ricci grabbed the edges of the navigator's table to keep from being hurled from his seat. One of his nails tore; I saw blood bloom brightly on his fingertip. He sucked it, inspected it, asked casually, "Why did we do that, sir?"

Craig's answer was terse and grim: "I'll show you." He swung the daysider around in a tight circle, stationed it well above the rim of the caldera. "Look down there."

Ricci half rose to see over Craig's shoulder. "Mother of God!" he breathed, and crossed himself rapidly.

Craig flicked on the intercom. "Anderson! Are the engines all right?"

A box on the rear wall crackled a reply, a brief splurge of technical details which amounted to "More or less."

I stood riveted to the spectacle beyond the window. A rift had burst open in the caldera's crater-pocked floor. Duty belatedly galvanized me into action. I sprang to my instruments. Even as I struggled to adjust them the chasm went on opening, wider and wider, jagged and enormous. Superheated gas and steam puffed out and dissipated in seconds. Dust and debris hurtled up at us, smashed down again to form a thickening carpet of slag and cinders.

Lava welled up in the rift; overflowed. A scalding torrent of liquid rock seethed out as freely as boiling water. It lapped around the crumbling rims of disintegrating craters. It tunneled under loose-lying ash, gulped beds of flickering embers. It sank again. The walls of the chasm reappeared, slimy-bright and dripping. Incandescent lava still gouted from innumerable tiny vents and fissures.

My instruments could not operate accurately from such a height. "Go lower! Go lower!" I shouted.

"No," said Craig.

"For Christ's sake, do as I bloody say! Every second I'm stuck up here, invaluable data is lost. That rift is being acted upon by colossal, ever-changing pressures—"

"Exactly," Craig agreed dryly. "That's why we're not descending."

"But such an opportunity may never recur! You're wasting—"

"No!" It was point-blank refusal.

I gritted my teeth in fury.

"I'm responsible for your safety," Craig reminded me.

"To hell with safety, I've got a job to do! I can't do it if you whisk me away the moment things get interesting. I need to be right up close to record—"

"Shut up!" roared Craig.

I shut up, but merely to marshal a new, more telling, blast.

Craig gave me no time to start again. "You're welcome to kill yourself," he said with brutal bluntness. "But you'll do it on Earth, not here. We've lost one daysider already. You're not murdering this one's crew."

I subsided. I was shaking.

Ricci grinned, openly enjoying my skirmish with the commander. I'd have wiped that smirk off his face with my fist, had civilized conventions not restrained me.

We continued with the systematic scan. It wasn't easy. My work demanded steady hands. Mine were slippery with sweat and, ten minutes later, still quivering.

Craig cleared his throat. "Tell me, Dr. Collins"—his voice carried just the right degree of interest—"have you hatched any theories yet to explain Mercury's volcanism?"

I forced my mind into clinical detachment, hunted for words which a layman would understand. "It must be something to do with the nearness, of the sun. At perihelion particularly, the sun's gravitational pull is tremendous. It must set up intolerable stresses in the planet's crust." I was warming nicely to my subject. Enthusiastically I continued: "Even if Mercury lacks plates of the terrestrial kind—and the evidence suggests that it does, although it may have some other mechanism to take their place—gravitational strain could set up tidal movements in the crust. This could riddle the hot spots with active quasi-plate boundaries. Friction would generate heat enough to melt the underlying rocks into magma. Sections of the crust would grind together, or dive under each other, or stretch apart allowing mantle material to well up under explosive pressure. Mascons would form—that is, massive concentrations of dense and heavy material gathered in pockets below the surface." I pointed to the printouts. "Those things imply that the mascon associated with our rift is rich in uranium ore. If it can be mined while the hot spot traverses the nightside . . ."

"Whoa, stop, stop!" Craig protested, chuckling. "You've lost me. I can't follow—"

"But it's so simple—"

"To a boffin, perhaps. Not to an old space dog like me."

Suddenly I felt like a fish, airborne and floundering. Once hooked by one's own eloquence, it is incredibly difficult to let go. I managed it somehow, and resolved to be more wary in future. If I could learn to refuse the bait, I might—just might!—avoid transformation into a raging bore.

Later, much later, I remembered that Craig knew more about Mercury than I did. All Space Service personnel were grounded in planetology. Craig would easily understand the weird effects of this killer world's eccentric orbit. With a shock I saw how skillfully he had handled me. His question had been designed to soothe my tight-strung nerves.

Another hour crawled by. Fatigue was beginning to blunt my reactions, to suck skill from my fingers and clarity from my mind. I wiped my sleeve across my smarting eyes and told Craig that a brief rest was essential.

Craig set the daysider to hover high above the treacherous ground, then paced the cabin, easing his cramped muscles. Ricci fetched sandwiches and coffee. I flipped through the printouts, partly to quench my curiosity, partly to insure that adequate data was being recorded. It was; the information on these tapes would fuel fierce battles among the experts for years.

I put the printouts aside. It was time to get on with the job. The daysider swooped down. We spent a further hour gambling for knowledge with our lives.

I became aware of Kraig and Anderson talking on the intercom. The words refrigeration unit were tossed to and fro. Ours was apparently on the blink, but Anderson was nursing it along. I listened, but soon ceased to pay attention.

Something odd was registering on the instruments.

"Ninety degrees to starboard, sir," Ricci told the commander. "Cut forward motion and hover," I said in the same breath.

The daysider slid smoothly to a stop. "Found something interesting?" asked Craig.

"I'm not sure. I'm trying to pinpoint it." A few minutes later, "Got it!" I announced with satisfaction. "Can we go down closer?"

We could and did, after a flurry of confusion when my directions proved off-beam.

We hovered a hundred yards above the anomaly. I squeezed past my equipment and pressed to the window, as near as its heat allowed. I squinted down through screwed-up eyes, probing a desert of rubble rotted and half liquefied by the unshielded radiation of the gigantic sun.

"See anything?" inquired Craig. Long since, he had given up trying to persuade me to keep back from the window.

I shook my head. "No, there's nothing to account for the readings I'm getting. Nothing visible, at least."

"I might be able to help if you explain your readings. Can you, without getting too technical?"

I pondered. "There's something down there which doesn't belong," I said at last. "Listen: suppose on Earth you get a limestone plateau with a bloody great lump of chalk in the middle. The nearest chalk outcrops are fifty miles away. You wonder how the chalk got there, right?"

"Right," Craig agreed.

"On Earth, of course, the chalk could have been moved in dozens of ways—by mankind, for one. Mercury's dead, however; we and the Base personnel are the only living beings here—unless you believe in ghosts!" I added with heavy jocularity . . . and trailed off, abruptly.

Craig's vivid blue glance flicked to my face. He made to speak and checked himself at once.

My feeble attempt at wit had sparked a strange unease in me. What had I told Craig? Nothing momentous; merely a stupid crack about ghosts . . .

Ghosts on Mercury. Of what—or whom?

My fingers crisped on the window-frame, clutching so tightly that the nails whitened. I stared out. The wasteland stared back at me, flashing a million scalpels into my eyes.

I blundered among my apparatus, examining meter readings with feverish haste. Clumsily I detached the printouts from the recorders. I juggled mentally with neat columns of figures and symbols. The anomaly stood out starkly, all the more starkly because the area was passing through a quiescent phase. Not that such a phase could last for long; inexorable pressures underthrust the entire region. The recent past must have seen scarifying tectonic upheavals.

I returned to the anomaly. Slowwitted with tension, I analyzed the elements which composed it. I fitted them together jigsaw-style, seeking connections, trying to construct an orderly whole . . .

Every drop of blood drained from my face; I felt it go.

Craig snapped out crisply, "Well?"

I turned my head away, half hoping to disguise my reaction.

Craig was not fooled. His voice hardened: "Come on, man, spit it out. You've gone as white as paper. Why?"

I said, "I've found your missing daysider." My voice sounded absurdly conversational.

"Where?"

"Down there."

"Show me."

I turned back to the window. I raked my gaze over fuming mineral pools and glutinous boulders. Somewhere among them was the wreck of the daysider. I could not find it. My eyes burned and watered. The stonescape began to waver, distorted by the tears clinging to my lashes. Pools and boulders took on an eerie beauty, rippling and sparkling, alive with iridescent light. I dried my eyes roughly on my sleeve and tried again. Slowly, carefully, shifting from blob to viscid blob, I searched that scene of hideous desolation.

I failed. I checked my instruments, trying to fix the daysider's exact location. I looked through the window again. And shivered.

Craig said quietly, "You've spotted it, haven't you? Show me."

I bit back horror. "I can't."

"Why not?"

"You won't recognize it. It doesn't look like a daysider any more."

Silence clamped down, brief but heart-stopping.

Harshly Craig ordered me: "Explain yourself."

"Very well. The daysider has fused into the ground. The upmost rock-layer is partly fluid and partly plastic, you know, and reaches appallingly high temperatures. The daysider must have crash-landed and sunk in. Direct contact with the ground has melted it, little by little probably, from the bottom up. The heat-shield is still intact, but discolored and sagging out of shape. One more perihelion passage should finish it altogether."

I stopped. I swallowed painfully. "In future it might be better to extend the heat-shields under the daysiders. That would protect their bottoms from the ground as well as their tops from the sun—" I fought rising nausea. "Oh Jesus no! A daysider crashes, it's doomed! The crew can't escape. They're trapped. They fry. Protection would spin out their agony—"

Craig sliced a hand down, cutting me off sharply. "Thank you, Dr. Collins. You can leave the rest to our imaginations."

Ricci's voice sounded behind us, unnaturally subdued: "What could have caused the crash?"

Craig cocked a grizzled eyebrow at me. "Any pointers to that?"

I studied my instruments. "No. This area's quiescent—that is, it's as quiescent as any part of a hot spot can be. Of course, two perihelions ago, things were likely very different. A rift, a range of volcanic vents: if something of that sort opened up, the daysider could have been knocked out of the sky by flying debris, as we so nearly were . . . wait!"

"He's off again," murmured Ricci. He had shaken off the frightfulness of his colleagues' fate with disgraceful speed.

I combed the area yard by yard. There was no evidence of volcanic vents or cones in the immediate vicinity. A rift, therefore: it had to be a rift. There was no rift; but there was another mascon. I thought hard: Rifts can close as well as open; so, search for traces of a closed rift . . .

Tensely I turned to Craig. "Commander, can we circle this spot slowly?"

Craig nodded. "If you wish. But make it snappy, will you? Time's running out."

We circled. Ricci, teeth clenched, tried to keep track of our wayward meanderings. I hunted dead or dormant rifts. The sheer fascination of the task soon claimed me heart and soul. All other considerations faded and fled before the juggernaut of intellectual delight.

I found what I sought. "There!" I exclaimed in triumph.

"Where?" asked Craig.

"To our left. See that seam in the ground, running diagonally toward that clump of crystals?"

"Crystals?"

"Yes. Look, over there: see where I'm pointing? Giant crystals, scintillating like jewels, every facet ablaze. Can't you see them?"

Craig frowned. "I see the crystals. But no seam."

"Well, it's not exactly a seam," I admitted. "It's a very faint, puckered, waggly line, smudged in places and nonexistent in others. According to my instruments, it marks the site of a closed rift. Not too recently closed, either, or all trace of it would have vanished. What's the betting it burst open two perihelions ago?"

As I spoke, shock hit me, shock at my blithe and gleeful tones. This was the rift which might have destroyed a daysider, might have condemned my fellow human beings to a lingering, agonizing death on this nightmare world millions of miles from home. Ashamed, I added soberly, "I'd appreciate a closer look at it. May we go lower?"

Craig slanted me a narrowed glance. "Is it safe?"

"Yes, as far as anything's safe here."

"Check your strain gauge."

"I just did. The needles are fluctuating, but not over a dangerously wide range."

We floated down to a point some fifty yards above the seam. With difficulty we tracked it, losing it from time to time and casting about to pick it up again. On one of these casts, I noticed a curious shadow on the ground.

"Hover," I said.

We hovered.

I peered into the monocular. Scorching radiance lashed back at me. My eyes had taken such a battering from the reflected sun-glare that they had lost all sensitivity. I could distinguish no details at all. I pushed the monocular aside. "We'll have to go lower," I advised.

"Is it absolutely necessary?" asked Craig.

"I'm afraid so. There's something down there and I can't make out what it is."

"Your instruments will tell you." I checked their readings. "They don't. All they show is a gravitational disequilibrium indicating a mascon below the surface. That shadow doesn't register at all."

"Then it's probably nothing." Craig sounded almost relieved.

"Nonsense," I snorted. I scowled at the inexplicable patch, dark only through contrast with the searing brightness all around it. "That shadow may not register because it's so small: nine or ten inches wide . . . and situated plumb on the seam." Excitement dried my mouth. "That means it must be connected with the rift. A shadow? It can't be a shadow, there's nothing to cast it. It must be—hell and damnation, I can't investigate it from this height. Please go lower!"

"No, Doctor. It's too risky."

You take hair-raising risks. My lips tightened at the memory of the rebuke. "Commander, this entire expedition is one big risk. If danger frightens you so badly, you should have stayed at home. The hot spot is no place for a coward."

Craig flushed. "It's common sense guiding me, not cowardice." "Then common sense should tell you that, in a stable zone, one may approach the ground in relative safety." I smiled at him. "Besides, you're forgetting: I'm the expert. I'm the one who knows what's safe and what's foolhardy. Now, will you let me do my job?"

Craig went very quiet. "All right," he said eventually. "As you say, you're the expert. But I think you're making a mistake." He concentrated on the controls.

I was elated with my victory . . . then.

The daysider drifted down another thirty yards. The shadow clarified into a perfect circle of red-tinged darkness.

"It's a vent," I said. "No wonder the instruments ignored it! They can't look into it. Nor can I. We're at the wrong angle. Can we move forward a little?"

"Madness," muttered Craig, but he took us forward. Now, at last, I could examine the vent properly. I set the recorders going, tucked myself into a corner by the window. I gazed down the narrow gullet. It plunged into the incandescent crust as straight as a die, dragging my sight down and down into a rich and glimmering blackness.

I surfaced and gave Craig a wry wisp of a grin, regretting my malicious attack. "I'm sorry, Commander, but I'm going to bash you."

For the first time I saw Craig startled out of his wits. "Eh?" he squawked.

I hastened to explain: "That pipeline's so tiny and so deep that I'll have to work from directly above it. That means hauling my gear right up to the window and dumping it all over the copilot's chair. You're bound to get clonked. Sorry."

Craig gestured Ricci out of his seat behind the navigator's table. "Up, lad. Help him."

Together Ricci and I manhandled to the window those items I needed. We wedged them between my chair and the control-board. Craig suffered the occasional thump without complaint. There was desperately little space. Cables trailed everywhere. It was a miracle that Ricci and I didn't trip and smash the lot.

Pinned among my gear at the window, I settled down as best I could, hunching my body in a vain effort to escape the brilliance blasting up from the ground. I made sure that the recorders were functioning unjarred by their rough handling, and wondered. How deep would this vent prove to be? What was its etiology? The seam which had spawned it overlay a mascon. What was the mascon's composition? Was it a brutally compressed intrusion of magma, like the first, or of—what? I had no idea.

Did the vent—could any vent!—pierce deeply enough to tap the mascon? If it did, why had the savagely crushed material not jetted upward, stoppering its safety valve with congealing melt? My instruments showed the mascon to be extremely hot and dense, and (judging distance by planetary scale) relatively near the surface. Yet the area was quiescent—so my readings showed. It didn't make sense. That mascon ought to be a seething inferno, dragged into renewed activity by the gravitational pull of the perihelion sun.

Why was the vent so straight?

A prickle of unease ran up my spine.

The crust at Mercury's hot spot was in constant, albeit sluggish, motion, powered by the nuclear horror ravening overhead. Plastic flow should have warped that pipeline out or true. It had not, which could mean only one thing: the vent was very recent indeed. Its lifespan was measurable in hours—or minutes.

I thought of the other mascon, of the other rift whose violent bursting had almost scooped us out of the sky. I twisted to check the strain gauge. Its needles were vibrating rapidly, but held within the limits for safety.

I stood locked in indecision. I felt a nerve jumping in my cheek.

Craig's glance fastened on my face, as penetrating as a laser. "What's wrong, Doctor?" he demanded.

I made a helpless gesture. "Nothing. According to my instruments this area is stable. But . . ." I fumbled for words which would not brand me as a crackpot, shying at fancies. "I'm not happy. Let's move."

Craig said dryly, "For once we're in agreement!" He pulled levers. Nothing happened. He tried them again, this time very gently. Still nothing. He pressed a button and, holding it down, gave the master lever a sharp hard jerk. The daysider remained poised above the vent. Poised? Almost imperceptibly it was beginning to settle. Its shadow grew. The vent, dead center, aimed straight at us like a weapon.

Craig reached for the intercom. Before his fingers touched it, it squealed. He flicked a switch, leaned toward the mouthpiece. "Why aren't the controls responding, Anderson?"

The engineer's voice answered tersely: "Sir, we're in trouble. The refrigeration unit has broken down completely. A section of the fuel system has jammed with the heat."

"Can you rig a bypass?" asked Craig.

Silence, punctured by faint clanks and rattles. Then: "Probably. It may not work."

"How soon can you rig it?"

"An hour."

Craig looked at me. "Have we got an hour?"

I lifted my shoulders. "God knows."

"Just how dangerous is that vent?"

My glance traveled to the strain gauge, to the pressure gauge. No danger at all ... which merely heightened my inexplicable anxiety. I repeated, "God knows."

Craig spoke into the intercom. "Hear that, Anderson?"

"Yes." The alarm in the engineer's voice came through clearly.

"Do you need help?" Craig inquired.

"No thanks. Explaining things to a helper would slow me down. I can work faster alone."

"As you wish. Rig that bypass as soon as possible. But first, stop us sinking or we'll end up stuck on that hole like a cap on a bottle. Can you do it?"

"I'll try."

Craig broke the connection.

I checked my apparatus, seeking malfunctions. If the heat had knocked out the daysider's fuel system, it could have affected my instruments as well, despite their independent power source. But no, all was normal, as far as I could tell.

My intuition continued to warn insistently of danger. Why?

I whipped around, snatched the printouts from the recorders. I raced down columns of data. Fright chilled me, for they told me nothing—yet I knew that, slowly but inexorably, pressure must be building in the unguessable dense layer at the bottom of the pipe.

Another thing I knew: this wasn't the only vent piercing the seam. It couldn't be. There had to be others, numerous others, some not yet fully formed, some stoppered tight. In turn they would relieve the unendurable pressure underground. Yet not one was active at this moment. Why not?

This was absurd. Here was I, a trained geologist, making the Error of Errors: relying on a hunch instead of on my equipment. Those gauges were far less fallible than a man's weak eyes and subjective brain. If they showed this zone to be stable, then stable it was.

I tried to relax. Instead, I started sweating profusely.

Craig divided his attention between me and the vent. Ricci gnawed his fingernails. We waited for the intercom to crackle, for Anderson to tell us we could leave.

The intercom stayed silent.

God, how I wished that I had heeded Craig's advice! But no: still bristling at his lecture about risk-taking, I had goaded him into stationing us here against his better judgment. That fit of childish pique of mine might well have doomed us all.

The heat, and our tension, climbed and climbed.

I tried to track my hunch to its source by reviewing my observations. From them had emerged the following theory: that hot spot vulcanism resulted from the colossal stresses set up in Mercury's crust by the drag of the sun. Excessive heating of the subsolar surface aided the formation of the volcanoes. My geologist's instinct clamored that I was right—which meant that tectonic activity in this region was governed by well-attested, long-proven laws. In turn this meant that I could trust my instruments. Indeed, I must, or all research was useless.

But Mercury was an alien planet, subject to alien laws. How dared I trust instruments designed on Earth? Anything could happen here: anything at all.

I turned to the window again. Our downward drift had stopped. We hung a few short yards above the vent, directly in its line of fire. All around, Mercury spread its flayed hide to the devouring sun. The vent was a worm-hole eating down to the bone. I peered into it, striving desperately to wrest the secret from that opalescent darkness. Something monstrous must be happening in that unimaginable nether world. We had to escape.

We could not escape. Realization broke through the barrier of exhaustion which dulled my mind: I understood our peril. My intuition sprang from an elementary physical fact which I should have remembered long ago. Funnel a broad, slow-flowing river into a narrow canyon, and it becomes a raging torrent. Similarly, in the mascon vast pressure stood within the safety limits because it was distributed throughout a vast area; but let that pressure force open a single narrow vent, and the gas-impregnated melt would explode.

I thought of warning Craig, but desisted. No practical purpose would be served thereby. I watched dials and meters, alert for the tiniest change. I watched the quiet vent.

I grew hideously frightened.

A pinpoint of luminescence seemed to glimmer faintly in the lowest depths of the pipe. I blinked, and it was gone. I strained and strained to glimpse it again . . . and there it was: fractionally brighter, fractionally larger—fractionally nearer. It was lunging upward like a bullet in a gun-barrel.

My nerve broke. "Get us away!" I yelled. My voice cracked into falsetto.

The daysider screamed forward, rising steeply; Craig had not waited to consult Anderson before engaging drive. Where was the point? We died ruptured by an engine-room explosion or impaled on a spear of flame: it made no difference.

We lived. We rocketed away from the danger zone, then slowed, then turned toward the now far distant place where the vent drilled down to the mascon.

"Holy Mother of God!" That was Ricci, hoarse with horror and awe.

Craig drew a deep breath, let it hiss out softly between his teeth.

A fountain of liquid metal punched five thousand feet into the sky. The top of the fountain splayed out like a blazing flower, white and gold against the backdrop of black vacuum. The petals curled, splitting into shafts of fire which plummeted unhindered to the smoking ground.

I reached for cameras and spectrosope. That jet of metal had to be captured on film, its constituents analyzed, its temperature recorded. I stooped to my task—and froze. Reaction hit me. I began to tremble violently.

Craig tried to raise Anderson on the intercom. There was no reply. "I'll go," said Ricci.

Some minutes later he returned.

"Anderson's collapsed, sir. The engine room's like a blast furnace, worse even than here. I've dragged him into the passage and chucked a bucket of water over him."

"Has he rigged a reliable fuel bypass?" Craig asked urgently.

"He's rigged something, heaven knows what. I burned my arm on it." Ricci indicated a charred patch on his sleeve.

"We'll risk a dash for the night-side," said Craig. He swung the daysider around, flogged it to its greatest possible speed. He looked near collapse himself. His bronzed face gleamed sickly pale under a varnish of perspiration.

Ricci sat down, reached for his charts. Quick and neat, he plotted our flight path. He offered few comments, few course corrections. So long as he kept track of our position, nightriders could be summoned to our rescue—provided that we reached the nightside. Where we reached it mattered little. Top priority was to escape the murderous sun.

We were traveling too fast for my equipment to function effectively, although my faith in it was restored. The facts it had revealed had been correct; I had failed to make the necessary deductions.

I shut down my apparatus, item by item; stowed it as neatly as I could against the wall. Thereafter my hands and my mind were empty. My imagination, free-wheeling, conjured the half-melted wreck of our sister craft. Its crew's fate still could be ours. We still might learn the full meaning of agony, still might smell our own flesh roasting as we died.

The daysider's motion grew erratic. Every so often it gave a tiny but sickening lurch. Certain engine components were beginning to run red-hot; soon they would seize up altogether.

I waited, rigid with suppressed panic. I was wretchedly aware of my body: of aching muscles, of labored breathing and pounding pulse, of sweat-drenched clothing clinging to my skin.

The hot spot fell away behind us. The terrain changed. We hurtled past crumbling crags and sword-edged pinnacles. Dully glowing shadows, stubby at first but lengthening, thrust toward a horizon which etched a line of jagged brightness on the sky.

My head throbbed excruciatingly. I curled into a ball with my hands covering my tortured eyes and my fingers digging into my hair. I had gazed too long upon the inhuman glory of the dayside. The price was pain: pain which the heat was aggravating beyond endurance.

Craig spoke. I don't know what he said; I wasn't listening; but the subject must have been me, for seconds later Ricci was at my side. From light-years away I heard his voice: "Come."

"Where?" I mumbled.

"Washroom."

Movement was impossible; pain paralyzed my will. I felt Ricci's slim strong fingers clamp around my wrists. I let him pull me from my chair, guide me across the cabin. I walked as gently as I could. If I jarred my splitting skull, it would burst into fragments.

One thing was clear: my work on Mercury was likely to remain unfinished. It had been intended that tomorrow, Earth-time, I should visit the hot spot lying at this moment frigid and inactive at the center of the nightside. My instructions were to locate its probable deposits of uranium ore. Even if I lived, the damage to my eyes would make me useless for a long while.

In the passage we almost stepped on Anderson. He was sprawled half lying, half leaning against the wall. He blinked at us blearily, but made no attempt to move out of our way.

Outside the washroom Ricci said, "Wait." I waited obediently. Tablets and a mug of water were thrust into my hands. "Get those inside you," Ricci ordered.

"What are they?"

"Pain-killers. Three."

I swallowed them. Relief came within minutes.

Ricci ran tepid water into the basin. "Dunk your head in that."

I dunked. The water was bliss. I stayed down until my starved lungs forced me to come spluttering up for air. Ricci passed me a towel. I used it, very gently, for it rasped like sandpaper. With difficulty I focused my light-scourged eyes on the mirror.

"Christ Almighty!" Shock jolted the oath out of me before I could catch my tongue.

Ricci reverted to his old provocative self. One of his eyebrows lifted wickedly. "Nice, isn't it? Think of the magnificent tan you'll have when that little lot dies down!"

That little lot was the king of all glare-burns. My face looked like raw red steak and felt as tight as a drum. It would blister splendidly tomorrow—if I had a tomorrow.

"Back at the Base we've a wonder-cream that will fix it in no time," Ricci told me cheerfully. "But mama mia, how you'll peel!"

I must have looked curious, for he laughed delightedly. "My God, Doc, you should have been an actor! You have the most expressive face I've ever seen!"

I refused the bait—which proved to be a mistake, since Ricci was hell-bent on making me explode. "It's a good job that looks can't kill," said he, "or I'd be dead at your feet by now." He grinned, his sardonic black eyes alight with mockery. "You're ideally suited to your work. Guess why!"

"Tell me," I said grimly. Nothing short of dynamite would stop him with a punch line begging to be delivered.

"You're a volcano yourself. Miniature, of course, but capable of spectacular eruptions. See! You're boiling up to one right now!" Abruptly I made for the passage. Ricci caught up with me, walked in silence at my side. Suddenly he said: "Odd how it affects one, isn't it? A brush with death, I mean. Particularly when every passing second increases its ghastliness."

I stood still, one foot poised for a step which was never taken. "Oh? Why?"

Ricci halted but kept his face averted. "Use your brain, Doc. The closer we get to the nightside, the cooler grows the ground, so, if we're forced down, the longer we'll take to die." His fingers linked into a knot which twisted tighter and tighter. "Know something? I've got a bad attack of the shakes. The absurd thing is, I seem to steady down more easily if someone else lets fly." His glance touched mine and darted away. "That's why I tried to provoke you. I—I wish I knew how to apologize."

On impulse I put my fist between Ricci's shoulder blades. Gruffly I said, "You're not the only one with the shakes." With rough gentleness I pushed him to the control cabin, prodded him toward his chair.

Lurching, juddering, the daysider streaked for the nightside. Our air grew acrid with the stink of smoldering insulation. Here was a new hazard: fire. Could the extinguishers cope, or would we suffocate in smoke . . . or burn alive?

Craig had smelled it too. His nostrils twitched. Terror brushed his face, to vanish at once behind a wall of unconcern. His slitted eyes scanned the control board. Without haste he pulled a knob. It must have connected with the ventilation system, for the acrid stench increased and fumes scraped my throat. I coughed.

Craig tapped the knob home again; reached for a small, bright red switch; threw it. A lever slipped its cogs and sprang up, jumping and rattling. Craig forced it down, held it in position by sheer brute strength. A light began to wink on the control board—a warning light which he ignored.

Ricci caught his breath. I looked around quickly. Our navigator's face was vivid with alarm.

"What have you done?" I asked Craig.

"Overridden the safety locks to give us more speed."

"That sounds bad."

"It is. Very." Craig glanced at the winking light. "As you can see, the engines hate it. They may well blow up. If so, I've killed us all."

The words should have been melodramatic. They were not; they were as cool as pebbles dredged from a lake in midwinter. Trying to match this coolness, I said: "So you're gambling, are you—gambling that you can get us to the nightside before we're ripped apart?"

"Yes."

I managed to smile. "Isn't that . . . a hair-raising risk?"

Craig kept his gaze fixed on the terrain ahead, but I saw him stiffen in startled understanding. "It is," he agreed. He added with a flash of wry humor, "I take your point."

Ricci butted in: "What point, sir?" To Ricci, who knew nothing of Craig's little lecture to me about risk-taking, our byplay was incomprehensible.

"Many jobs entail risks of one kind or another," Craig told him, and finished ruefully, "Eh, Dr. Collins?"

I gave a noncommittal grunt, aware that Craig's motives for risk-taking were different from mine.

Craig was acting from necessity, to save our lives. My motives were less worthy: I loved my work, but also the acclaim which sometimes followed. I was obsessed by curiosity to the point where human values took second place—except on the occasion when I had goaded Craig into positioning us above the vent: injured pride had precipitated that. I felt thoroughly ashamed of myself.

Craig must have sensed my discomfort. He flicked me a glance—friendly, mischievous, accompanied by a quick crooked grin: the last kind of glance I expected. He looked away before I could respond. I was thankful; at this very moment I was busy realizing that I had come to like and respect him more than I would have imagined possible. It was an odd sensation; I needed time to come to terms with it.

Ricci eyed us, his puzzlement increasing until he was one huge, obtrusive, silent question mark ... the crucial word being silent. I hoped to God that he would remain so; in the charged atmosphere which now prevailed, overt comment would be exquisitely embarrassing.

Ricci kept his mouth shut. Reluctantly he bent his attention to his navigation gear. The threat of a public soul-baring display was averted.

Slowly I relaxed. I concentrated on the scene tumbling past our window. Far ahead of us raced our shadow, an ever-changing blob which danced and bounded over the ravaged rockscape. I watched it, breathing shallowly, trying not to notice our vile air. Choke just once, and I would go on choking till I died.

"Two degrees to port, sir," husked Ricci.

"Two degrees to port," Craig repeated. He altered our course.

Behind us, bloated and ferocious, sank the sun. Our shadow fled further and further away. Came the blessed instant when it vanished permanently upward into the star-spiked darkness of the sky.

Ricci buried his head in his hands; then lowered them, busied himself with his charts. He assumed a calm and casual pose which was ruined through being grossly overplayed.

Craig slowed the daysider to a safer speed. The winking light went out. The juddering diminished. Craig tested the controls.

I croaked, "Will we survive?"

Craig studied me briefly. I avoided his gaze, too avid for reassurance to trust myself to meet those bright, tired eyes. "Probably," he answered. His voice held no emotion at all.

With unsteady fingers I rubbed my forehead, pushing back my soaked and tangled hair. The nightmare was finished: we would live: probably. I began at last to dare to contemplate the future.