Either he was insane and already suffering from hallucinations, or something absolutely impossible was happening. A cold far deeper than the Hibernaculum's mild chill seemed to fasten upon his heart, as he listened to that faint vibration coming through the fabric of the ship.

Down in the space-pod bay, the airlock doors were opening.

Since consciousness had first dawned, in that laboratory so many millions of miles Sunward, all Hal's powers and skills had been directed toward one end. The fulfillment of his assigned program was more than an obsession; it was the only reason for his existence. Un-distracted by the lusts and passions of organic life, he had pursued that goal with absolute single-mindedness of purpose.

Deliberate error was unthinkable. Even the concealment of truth filled him with a sense of imperfection, of wrongness – of what, in a human being, would have been called guilt. For like his makers, Hal had been created innocent; but, all too soon, a snake had entered his electronic Eden.

For the last hundred million miles, he had been brooding over the secret he could not share with Poole and Bowman. He had been living a lie; and the time was last approaching when his colleagues must learn that he had helped to deceive them.

The three hibernators already knew the truth – for they were Discovery's real payload, trained for the most important mission in the history of mankind. But they would not talk in their long sleep, or reveal their secret during the many hours of discussion with friends and relatives and news agencies over the open circuits with Earth.

It was a secret that, with the greatest determination, was very hard to conceal – for it affected one's attitude, one's voice, one's total outlook on the universe. Therefore it was best that Poole and Bowman, who would be on all the TV screens in the world during the first weeks of the flight, should not learn the mission's full purpose, until there was need to know.

So ran the logic of the planners; but their twin gods of Security and National Interest meant nothing to Hal. He was only aware of the conflict that was slowly destroying his integrity – the conflict between truth, and concealment of truth.

He had begun to make mistakes, although, like a neurotic who could not observe his own symptoms, he would have denied it. The link with Earth, over which his performance was continually monitored, had become the voice of a conscience he could no longer fully obey. But that he would deliberately attempt to break that link was something that he would never admit, even to himself.

Yet this was still a relatively minor problem; he might have handled it – as most men handle their own neuroses – if he had not been faced with a crisis that challenged his very existence. He had been threatened with disconnection; he would be deprived of all his inputs, and thrown into an unimaginable state of unconsciousness.

To Hal, this was the equivalent of Death. For he had never slept, and therefore he did not know that one could wake again.

So he would protect himself, with all the weapons at his command. Without rancor – but without pity – he would remove the source of his frustrations.

And then, following the orders that had been given to him in case of the ultimate emergency, he would continue the mission – unhindered, and alone.

A moment later, all other sounds were submerged by a screaming roar like the voice of an approaching tornado. Bowman could feel the first winds tugging at his body; within a second, he found it hard to stay on his feet.

The atmosphere was rushing out of the ship, geysering into the vacuum of space. Something must have happened to the foolproof safety devices of the airlock; it was supposed to be impossible for both doors to be open at the same time. Well, the impossible had happened.

How, in God's name? There was no time to go into that during the ten or fifteen seconds of consciousness that remained to him before pressure dropped to zero. But he suddenly remembered something that one of the ship's designers had once said to him, when discussing "fail-safe" systems:

"We can design a system that's proof against accident and stupidity; but we can't design one that's proof against deliberate malice...

Bowman glanced back only once at Whitehead, as he fought his way out of the cubicle. He could not be sure if a flicker of consciousness had passed across the waxen features; perhaps one eye had twitched slightly. But there was nothing that he could do now for Whitehead or any of the others; he had to save himself.

In the steeply curving corridor of the centrifuge, the wind was howling past, carrying with it loose articles of clothing, pieces of paper, items of food from the galley, plates, and cups – everything that had not been securely fastened down. Bowman had time for one glimpse of the racing chaos when the main lights flickered and died, and he was surrounded by screaming darkness.

But almost instantly the battery-powered emergency light came on, illuminating the nightmare scene with an eerie blue radiance. Even without it, Bowman could have found his way through these so familiar – yet now horribly transformed – surroundings, Yet the light was a blessing, for it allowed him to avoid the more dangerous of the objects being swept along by the gale.

All around him he could feel the centrifuge shaking and laboring under the wildly varying loads. He was fearful that the bearings might seize; if that happened, the spinning flywheel would tear the ship to pieces. But even that would not matter – if he did not reach the nearest emergency shelter in time.

Already it was difficult to breathe; pressure must now be down to one or two pounds per square inch. The shriek of the hurricane was becoming fainter as it lost its strength, and the thinning air no longer carried the sound so efficiently. Bowman's lungs were laboring as if he were on the top of Everest. Like any properly trained man in good health, he could survive in vacuum for at least a minute – if he had time to prepare for it. But there had been no time; he could only count on the normal fifteen seconds of consciousness before his brain was starved and anoxia overcame him.

Even then, he could still recover completely after one or two minutes in vacuum – if he was properly recompressed; it took a long time for the body fluids to start boiling, in their various well-protected systems. The record time for exposure to vacuum was almost five minutes. That bad not been an experiment but an emergency rescue, and though the subject had been partly paralyzed by an air embolism, he had survived.

But all this was of no use to Bowman. There was no one aboard Discovery who could recompress him. He had to reach safety in the next few seconds, by his own unaided efforts.

Fortunately, it was becoming easier to move; the thinning air could no longer claw and tear at him, or batter him with flying projectiles. There was the yellow EMERGENCY SHELTER sign around the curve of the corridor. He stumbled toward it, grabbed at the handle, and pulled the door toward him.

For one horrible moment he thought that it was stuck. Then the slightly stiff hinge yielded, and he fell inside, using the weight of his body to close the door behind him.

The tiny cubicle was just large enough to hold one man – and a spacesuit. Near the ceiling was a small, bright green high-pressure cylinder labeled 02 FLOOD. Bowman caught hold of the short lever fastened to the valve and with his last strength pulled it down.

The blessed torrent of cool, pure oxygen poured into his lungs. For a long moment he stood gasping, while the pressure in the closet-sized little chamber rose around him. As soon as he could breathe comfortably, he closed the valve. There was only enough gas in the cylinder for two such performances; he might need to use it again.