The Sentinel

by Arthur C. Clarke

  At any time the station on Venus could speak to the Star Queen, but there was so little that could be said. One could not with any decency give words of encouragement to men in the condemned cell, even when there was some slight uncertainty about the actual date of execution.

  So Venus contented itself with a few routine messages every day and blocked the stream of exhortations and newspaper offers that came pouring from Earth. As a result private radio companies on Earth made frantic attempts to contact the Star Queen directly. They failed, simply because it never occurred to Grant and McNeil to focus their receiver anywhere except on Venus, now so tantalizingly near at hand.

  There had been an embarrassing interlude when McNeil emerged from his cabin, but though relations were not particularly cordial, life aboard the Star Queen continued much as before.

  Grant spent most of his waking hours in the pilot’s position, calculating approach maneuvers and writing interminable letters to his wife. He could have spoken to her had he wished, but the thought of all those millions of waiting ears had prevented him from doing so. Interplanetary speech circuits were supposed to be private—but too many people would be interested in this one.

  In a couple of days, Grant assured himself, he would hand his letter to McNeil and they would decide what was to be done. Such a delay would also give McNeil a chance of raising the subject himself. That he might have other reasons for his hesitation was something Grant's conscious mind still refused to admit.

  He often wondered how McNeil was spending his time. The engineer had a large library of microfilm books, for he read widely and his range of interests was unusual. His favorite book, Grant knew, was Jurgen and perhaps even now he was trying to forget his doom by losing himself in its strange magic. Others of McNeil’s books were less respectable and not a few were of the class curiously described as “curious.”

  The truth of the matter was that McNeil was far too subtle and complicated a personality for Grant to understand. He was a hedonist and enjoyed the pleasures of life all the more for being cut off from them for months at a time. But he was by no means the moral weakling that the unimaginative and somewhat Puritanical Grant had supposed.

  It was true that he had collapsed completely under the initial shock and that his behavior was over the wine was—by Grant’s standards—reprehensible. But McNeil had had his breakdown and had recovered. Therein lay the difference between him and the hard but brittle Grant.

  Though the normal routine of duties had been resumed by tacit consent, it did little to reduce the sense of strain. Grant and McNeil avoided each other as much as possible except when mealtimes brought them together. When they did meet, they behaved with an exaggerated politeness as if each were striving to be perfectly normal—and inexplicably failing.

  Grant had hoped that McNeil would himself broach the subject of suicide, thus sparing him a very awkward duty. When the engineer stubbornly refused to do anything of the sort it added to Grant’s resentment and contempt. To make matters worse he was suffering from nightmares and sleeping very badly.

  The nightmare was always the same. When he was a child it had often happened that at bedtime he had been reading a story far too exciting to be left until morning. To avoid detection he had continued reading under the bedclothes by flashlight, curled up in a snug white-walled cocoon. Every ten minutes or so the air had become too stifling to breathe and his emergence into the delicious cool air had been a major part of the fun.

  Now, thirty years later, these innocent childhood hours returned to haunt him. He was dreaming that he could not escape from the suffocating sheets while the air was steadily and remorselessly thickening around him.

  He had intended to give McNeil the letter after two days, yet somehow he put it off again. This procrastination was very unlike Grant, be he managed to persuade himself that it was a perfectly reasonable thing to do.

  He was giving McNeil a chance to redeem himself—to prove that he wasn’t a coward by raising the matter himself. That McNeil might be waiting for him to do exactly the same thing somehow never occurred to Grant.

  The all-too-literal deadline was only five days off when, for the first time, Grant’s mind brushed lightly against the thought of murder. He had been sitting after the “evening” meal, trying to relax as McNeil clattered around in the gallery with, he considered, unnecessary noise.

  What use, he asked himself, was the engineer to the world? He had no responsibilities and no family—no one would be any the worse off for his death. Grant, on the other hand, had a wife and three children of whom he was moderately fond, though for some obscure reason they responded with little more than dutiful affection.

  Any impartial judge would have no difficulty in deciding which of them should survive. If McNeil had a spark of decency in him he would have come to the same conclusion already. Since he appeared to have done nothing of the sort he had forfeited all further claims to consideration.

  Such was the elemental logic of Grant’s subconscious mind, which had arrived at its answer days before but had only now succeeded in attracting the attention for which it had been clamoring. To Grant’s credit he at once rejected the thought with horror.

  He was an upright and honorable person with a very strict code of behavior. Even the vagrant homicidal impulses of what is misleadingly called “normal” man had seldom ruffled his mind. But in the days—the very few days—left to him, they would come more and more often.

  The air had become noticeably fouler. Though there was still no real difficulty in breathing, it was a constant reminder of what lay ahead, and Grant found that it was keeping him from sleep. This was not pure loss, as it helped to break the power of his nightmares, but he was becoming physically run down.

  His nerve was also rapidly deteriorating, a state of affairs accentuated by the fact that McNeil seemed to be behaving with unexpected and annoying calmness. Grant realized that he had come to the stage when it would be dangerous to delay the showdown any longer.

  McNeil was in his room as usual when Grant went up to the control cabin to collect the letter he had locked away in the safe—it seemed a lifetime ago. He wondered if he need add anything more to it. Then he realized that this was only another excuse for delay. Resolutely he made his way toward McNeil’s cabin.

  A single neutron begins the chain-reaction that in an instant can destroy a million lives and the toil of generations. Equally insignificant and unimportant are the trigger-events which can sometimes change a man’s course of action and so alter the whole pattern of his future.

  Nothing could have been more trivial than that which made Grant pause in the corridor outside McNeil’s room. In the ordinary way he would not even have noticed it. It was the smell of smoke—tobacco smoke.

  The thought that the sybaritic engineer had so little self-control that he was squandering the last precious liters of oxygen in such a manner filled Grant with blinding fury. He stood for a moment quite paralyzed with the intensity of his emotion.

  Then slowly, he crumpled the letter in his hand. The thought that which had first been an unwelcome intruder, then a casual speculation, was at last fully accepted. McNeil had had his chance and had proved, by his unbelievable selfishness, unworthy of it. Very well—he could die.

  The speed with which Grant had arrived at this conclusion would not have deceived the most amateurish of psychologists. It was relief as much as hatred that drove him away from McNeil’s room. He had wanted to convince himself that there would be no need to do the honorable thing, to suggest some game of chance that would give them each an equal probability of life.

  This was the excuse he needed, and he had seized upon it to salve his conscience. For though he might plan and even carry out a murder, Grant was the sort of person who would have to do it according to his own particular moral code.

  As it happened he was—not for the first time—badly misjudging McNeil. The engineer was a heavy smoker and tobacco was quite essential to his mental well-being even
in normal circumstances. How much more essential it was now, Grant, who only smoked occasionally and without much enjoyment, could never have appreciated.

  McNeil had satisfied himself by careful calculation that four cigarettes a day would make no measurable difference whatsoever to the ship’s oxygen endurance, whereas they would make all the difference in the world to his own nerves and hence indirectly to Grant’s.

  But it was no use explaining this to Grant. So he had smoked in private and with a self-control he found agreeably, almost voluptuously, surprising. It was sheer bad luck that Grant had detected one of the day’s four cigarettes.

  For a man who had only at that moment talked himself into murder, Grant’s actions were remarkably methodical. Without hesitation, he hurried back to the control room and opened the medicine chest with its neatly labeled compartments, designed for almost every emergency that could occur in space.

  Even the ultimate emergency had been considered, for there behind its retaining elastic bands was the tiny bottle he had been seeking, the image of which had been lying hidden far down in the unknown depths of his mind through all these days. It bore a white label carrying a skull-and-crossbones, and beneath them the words: Approx. one-half gram will cause painless and almost instantaneous death.

  The poison was painless and instantaneous—that was good. But even more important was a fact unmentioned on the label. It was also tasteless.

  The contrast between the meals prepared by Grant and those organized with considerable skill and care by McNeil was striking. Anyone who was fond of food and who spent a good deal of his life in space usually learned the art of cooking in self-defense. McNeil had done this long ago.

  To Grant, on the other hand, eating was one of those necessary but annoying jobs which had to be got through as quickly as possible. His cooking reflected this opinion. McNeil had ceased to grumble about it, but he would have been very interested in the trouble Grant was taking over in this particular meal.

  If he noticed any increasing nervousness on Grant’s part as the meal progressed, he said nothing. They ate almost in silence, but that was not unusual for they had long since exhausted most of the possibilities of light conversation. When the last dishes—deep bowls with inturned rims to prevent the contents drifting out—had been cleared away, Grant went into the gallery to prepare the coffee.

  He took rather a long time, for at the last moment something quite maddening and quite ridiculous happened. He suddenly recalled one of the film classics of the last century in which the fabulous Charlie Chaplin tried to poison an unwanted wife—and then accidentally changed the glasses.

  No memory could have been more unwelcome, for it left him shaken with a gust of silent hysteria. Poe’s Imp of the Perverse, that demon who delights in defying the careful canons of self-preservation, was at work and it was a good minute before Grant could regain his self-control.

  He was sure that, outwardly at least, he was quite calm as he carried in the two plastic containers and their drinking-tubes. There was no danger of confusing them, for the engineer’s had the letters MAC painted boldly across it.

  At the thought Grant nearly relapsed into psychopathic giggles but just managed to regain control with the somber reflection that his nerves must be in even worse condition than he had imagined.

  He watched, fascinated, though without appearing to do so, as McNeil toyed with his cup. The engineer seemed in no great hurry and was staring moodily into space. Then he put his lips to the drinking tube and sipped.

  A moment later he spluttered slightly—and an icy hand seemed to seize Grant’s heart and hold it tight. Then McNeil turned to him and said evenly, “You’ve made it properly for once. It’s quite hot.”

  Slowly, Grant’s heart resumed its interrupted work. He did not trust himself to speak, but managed a noncommittal nod. McNeil parked the cup carefully in the air, a few inches away from his face.

  He seemed very thoughtful, as if weighing his words for some important remark. Grant cursed himself for having made the drink so hot—that was just the sort of detail that hanged murderers. If McNeil waited much longer he would probably betray himself through nervousness.

  “I suppose,” said McNeil in a quietly conversational sort of way, “it has occurred to you that there’s still enough air to last one of us to Venus?”

  Grant forced his jangling nerves under control and tore his eyes away from that hypnotic cup. His throat seemed very dry as he answered, “It—it had crossed my mind.”

  McNeil touched his coffee cup, found it still too hot and continued thoughtfully, “Then wouldn’t it be more sensible if one of us decided to walk out of the airlock, say—or to take some of the poison in there?” He jerked his thumb toward the medicine chest, just visible from where they were sitting.

  Grant nodded.

  “The only trouble, of course,” added the engineer, “is to decide which of us will be the unlucky one. I suppose it would have to be picking a card or in some other quite arbitrary way.”

  Grant stared at McNeil with fascination that almost outweighed his nervousness. He had never believed that the engineer could discuss the subject so calmly. Grant was sure he suspected nothing. Obviously McNeil’s thoughts had been running on parallel lines to his own and it was scarcely even a coincidence that he had chosen this time, of all times, to raise the matter.

  McNeil was watching him intently, as if judging his reactions.

  “You’re right,” Grant heard himself say. “We must talk it over.”

  “Yes,” said McNeil quite impassively. “We must.” Then he reached for his cup again, put the drinking tube to his lips and sucked slowly.

  Grant could not wait until he had finished. To his surprise the relief he had been expecting did not come. He felt a stab of regret, though it was not quite remorse. It was a little late to think of it now, but he suddenly remembered that he would be alone in the Star Queen, haunted by his own thoughts, for more than three weeks before the rescue came.

  He did not wish to see McNeil die, and he felt rather sick. Without another glance at his victim he launched himself toward the exit.

  Immovably fixed, the fierce sun and the unwinking stars looked upon the Star Queen, which seemed as motionless as they. There was no way of telling that the tiny dumbell of the ship had now almost reached her maximum speed and that millions of horsepower were claimed within the small sphere, waiting for the moment of its release. There was no way of telling, indeed, that she carried any life at all.

  An airlock on the night-side of the ship slowly opened, letting a blaze of light escape from the interior. The brilliant circle looked very strange hanging there in the darkness. Then it was abruptly eclipsed as two figures floated out of the ship.

  One was much bulkier than the other, and for a rather important reason—it was wearing a space-suit. Now there are some forms of apparel that may be worn or discarded as the fancy pleases with no other ill-effects than a possible loss of social prestige. But space-suits are not among them.

  Something not easy to follow was happening in the darkness. Then the smaller figure began to move, slowly at first but with rapidly mounting speed. It swept out of the shadow of the ship into the full blast of the sun, and now one could see that strapped to its back was a small gas-cylinder from which a mist was jetting to vanish almost instantly into space.

  It was a crude but effective rocket. There was no danger in that the ship’s minute gravitational pull would drag the body back into it again.

  Rotating slightly, the corpse dwindled against the stars and vanished from sight in less than a minute. Quite motionless, the figure in the airlock watched it go. Then the outer door swung shut, the circle of brilliance vanished and only the pale Earthlight still glinted on the shadowed wall of the ship.

  Nothing else whatsoever happened for twenty-three days.

  The captain of the Hercules turned to his mate with a sigh of relief.

  “I was afraid he couldn’t do it. It must have
been a colossal job to break his orbit single-handed—and with the air as thick as it must be by now. How soon can we get to him?”

  “It will take about an hour. He’s still got quite a bit of eccentricity but we can correct that.”

  “Good. Signal the Leviathan and Titan that we can make contact and ask them to take off, will you? But I wouldn’t drop any tips to your news commentator friends until we’re safely locked.”

  The mate had the grace to blush. “I don’t intend to,” he said in a slightly hurt voice as he pecked delicately at the keys of his calculator. The answer that flashed instantly on the screen seemed to displease him.

  “We’d better board and bring the Queen down to circular speed ourselves before we call the other tugs,” he said, “otherwise we’ll be wasting a lot of fuel. She’s still got a velocity excess of nearly a kilometer a second.”

  “Good idea—tell Leviathan and Titan to stand by but not to blast until we give them the new orbit.”

  While the message was on its way down through the unbroken cloudbanks that covered half the sky below, the mate remarked thoughtfully, “I wonder what he’s feeling like now?”

  “I can tell you. He’s so pleased to be alive that he doesn’t give a hoot about anything else.”

  “Still, I’m not sure I’d like to have left my shipmate in space so that I could get home.”

  “It’s not the sort of thing that anyone would like to do. But you heard the broadcast—they’d talked it over calmly and the loser went out of the airlock. It was the only sensible way.”

  “Sensible perhaps—but it’s pretty horrible to let someone else sacrifice himself in such a cold-blooded way so that you can live.”

  “Don’t be a ruddy sentimentalist. I’ll bet that if it happened to us you’d push me out before I could even say my prayers.”