At least, he reflected, the primary mission of the backpack computer was to protect itself, which meant keeping the organic part of Roger Torraway alive. It might steal energy from the part that would keep him sane: deprive him of communications, interfere with his perceptions. But he was sure he would get back to the lander alive.

If perhaps crazy.

He was more than halfway back already, he was nearly sure. And he was still sane. The way to keep sane was to keep from worrying. The way to keep from worrying was to think of other things. He imagined Sulie Carpenter’s bright presence, only days away; wondered if she was serious about staying on Mars. Wondered if he was himself. He reminisced within himself about great meals he had eaten, the spinach-green pasta in the cream sauce in Sirmione, overlooking the bright transparent water of Lake Garda; the Kobe beef in Nagoya; the fire-hot chili in Matamoras. He thought of his guitar and made a resolve to haul it out and play it. There was too much water in the air under the domes to be good for it, and Roger did not much like to be in the lander; and outside in the open, of course, its sound was strange because it was all bone-conducted. But still. He rehearsed the fingering of chords, modulating through the sharps and sevenths and minors. He imagined his fingers fretting the E-minor, the D, the C and the B-seventh of the opening passages of “Greensleeves,” and hummed along with them inside his head. Sulie would enjoy singing along with the guitar, he thought. It would make the cold Martian nights pass—

He snapped to alertness.

This Martian night was no longer passing quite so quickly.

Subjectively it seemed as though his gait had slowed from a race to a steady stride; but he knew that that had not changed, his time perception had stretched back to normal, maybe even a bit slower than normal: he seemed to be walking quite slowly and methodically.

Why?

There was something ahead of him. At least a kilometer away. And very bright.

He could not make it out.

A dragon?

It seemed to leap toward him, breathing a long tongue of light like flame.

His body stopped walking. It dropped to its knees and began to crawl, very slowly, keeping down.

This is insane, he said to himself. There are no dragons on Mars. What am I doing? But he could not stop. His body inched along, knee and opposite hand, hand and opposite knee, into the shelter of a hummock of sand. Carefully and quickly it began to scoop the powdery Martian soil away, to fit itself into the hollow, scraping some of the dirt back over itself. Inside his head tiny voices were babbling, but he could not understand what they said: they were too faint, too garbled.

The dragon slowed and stopped a few dozen meters away, its tongue of frozen flame lolling out toward the mountains. His vision clouded and changed; now the flame was dimmed, and the bulk of the thing itself came up in ghostly luminescence. Two smaller creatures were dropping off its back, ugly, simian beasts that hulked along and exuded menace with every gesture.

There were no dragons on Mars, and no gorillas either.

Roger summoned up all of his energies. “Don!” he shouted. “Brad!”

He was not getting through.

He knew that the backpack-brother was still withholding energy from the transmitter. He knew that his perceptions had been skewed, and that the dragon was no dragon and the gorillas no gorillas. He knew that if he could not override the brother on his back something very bad was likely to happen, because he knew that his fingers were slowly and delicately wrapping themselves around a chunk of limonite the size of a baseball.

And he knew that he had never been closer to going mad in his life than he was right now.

Roger made an immense effort to recapture his sanity.

The dragon was no dragon. It was the Mars vehicle.

The apes were not apes. They were Brad and Don Kayman.

They were not threatening him. They had come all this way in the flint-cold Martian night to find him and help him.

He repeated the truths over and over, like a litany; but whatever he thought he was powerless to prevent what his arms and body did. They seized the chunk of rock; the body raised itself up; the arms threw the rock with exact precision into the headlight of the crawler.

The long tongue of frozen flame winked out.

The light from the million fiery stars was ample for Roger’s senses, but it would be very little help to Brad and Don Kayman. He could see them (still gorilloid, still menacing of mien) stumbling at random; and he could feel what his body was doing.

It was creeping toward them.

“Don!” he shouted. “Watch out!” But the voice never left his skull.

This was insanity, he told himself. I have to stop!

He could not stop.

I know that’s not an enemy! I don’t really want to hurt them—

And he kept on advancing.

He was almost sure he could hear their voices now. So close, their transmitters would be deafening in his perceptions under normal conditions, without the intercession of the automatic volume control. Even cut off as he was, there was some spillage.

“—round here somewh—”

Yes! He could even make out words; and the voice, he was sure, had been Brad’s.

He shouted with all the power at his command: “Brad! It’s me, Roger! I think I’m trying to kill you!”

Heedless, his body kept up his steady crawl. Had they heard him? He shouted again; and this time he could see both of them stop, as though listening to the faintest of distant cries.

The tiny thread of Don Kayman’s voice whispered: “I’m sure I heard him that time, Brad.”

“You did!” howled Roger, forcing his advantage. “Watch out! The computer has taken over. I’m trying to override it, but — Don!” He could recognize them now, by the stiffly outstretched arm of the priest’s pressure suit. “Get away! I’m trying to kill you!”

He could not make out the words; they were louder, but both men were shouting at once and the result was garble. His body was not affected; it continued its deadly stalk.

“I can’t see you, Roger.”

“I’m ten meters away from you — south? Yes, south! Crawling. Low down to the ground.”

The priest’s faceplate glittered in the starlight as it swung toward him; then Kayman turned and began to run.

Roger’s body gathered itself up and began a leap after the priest. “Faster!” Roger shouted. “Oh, Christ! You’ll never get away—” Even uncrippled, even in daylight, even without the impediment of the suit, Kayman would have had no chance to escape Roger’s smoothly functioning body. Under the actual circumstances running was a waste of time. Roger felt his power-driven muscles gather themselves for a spring, felt his hands claw out to grasp and destroy—

The universe spun around him.

Something had struck him from behind. He plowed forward on his face; but his instant reflexes had him half turning even as he fell, clawing at the thing that had leaped on his back. Brad! And he could feel Brad struggling frantically with something — with some part of the—

And the greatest pain of all struck him; and he lost consciousness like the snapping off of a switch.

There was no sound. There was no light. There was no feeling of touch, or smell or taste. It took a long time for Roger to realize that he was conscious.

Once, as an undergraduate in a psychology miniseminar, he had volunteered for an hour in a sensory-deprivation tank. It had seemed forever, with no sensations coming in at all, nothing but the very faint and unobtrusive housekeeping sounds of his own body: soft thud of pulse, sighing stirring in his lungs. Now there was not even that much.

For a long time. He could not guess how long.

Then he perceived a vague stirring in his personal interior space. It was a strange sensation, hard to identify; as though liver and lungs were gently changing places. It went on for some time, and he knew that something was being done to him. He could not tell what.