In the end, any particular planet must die. It may be a quick death as its sun explodes. It may be a slow death, as its sun sinks into decay and its oceans lock in ice. In the latter case, at least, intelligent life has a chance of survival.

The direction of survival may be outward into space, to a planet closer to the cooling sun or to a planet of another sun altogether. This particular avenue is closed if the planet is unfortunate enough to be the only significant body rotating about its primary and if, at the time, no other star is within half a thousand light-years.

The direction of survival may be inward, into the crust of the planet. That is always available. A new home can be built underground and the heat of the planet's core can be tapped for energy. Thousands of years may be necessary for the task, but a dying sun cools slowly.

But planetary warmth dies, too, with time. Burrows must be dug deeper and deeper until the planet is dead through and through.

The time was coming.

On the surface of the planet, wisps of neon blew listlessly, barely able to stir the pools of oxygen that collected in the lowlands. Occasionally, during the long day, the crusted sun would flare briefly into a dull red glow and the oxygen pools would bubble a little.

During the long night, a blue-white oxygen frost formed over the pools and on the bare rock, a neon dew formed.

Eight hundred miles below the surface, a last bubble of warmth and life existed.

Wenda's relationship to Roi was as close as one could imagine, closer by far than it was decent for her to know.

She had been allowed to enter the ovarium only once in her life and it had been made quite clear to her that it was to be only that once.

The Raceologist had said, “You don't quite meet the standards, Wenda, but you are fertile and we'll try you once. It may work out.”

She wanted it to work out. She wanted it desperately. Quite early in her life she had known that she was deficient in intelligence, that she would never be more than a Manual. It embarrassed her that she should fail the Race and she longed for a single chance to help create another being. It became an obsession.

She secreted her egg in an angle of the structure and then returned to watch. The “randoming” process that moved the eggs gently about during mechanical insemination (to insure even gene distribution) did not, by some good fortune, do more than make her own wedged-in egg wobble a bit

Unobtrusively she maintained her watch during the period of maturation, observed the little one who emerged from the particular egg that was hers, noted his physical markings, watched him grow.

He was a healthy youngster and the Raceologist approved of him.

She had said once, very casually, “Look at that one, the one sitting there. Is he sick?”

“Which one?” The Raceologist was startled. Visibly sick infants at this stage would be a strong reflection upon his own competence. “You mean Roi? Nonsense. I wish all our young were like that one.” I

At first, she was only pleased with herself, then frightened, finally horrified. She found herself haunting the youngster, taking an interest in his schooling, watching him at play. She was happy when he was near, dull and unhappy otherwise. She had never heard of such a thing, and she was ashamed.

She should have visited the Mentalist, but she knew better. She was not so dull as not to know that this was not a mild aberration to be cured at the twitch of a brain cell. It was a truly psychotic manifestation. She was certain of that. They would confine her if they found out. They would euthanase her, perhaps, as a useless drain on the strictly limited energy available to the race. They might even euthanase the offspring of her egg if they found out who it was.

She fought the abnormality through the years and, to a measure, succeeded. Then she first heard the news that Rio had been chosen for the long trip and was filled with aching misery.

She followed him to one of the empty corridors of the cavern, some miles from the city center. The city! There was only one.

This particular cavern had been closed down within Wenda's own memory. The Elders had paced its length, considered its population and the energy necessary to keep it powered, then decided to darken it. The population, not many to be sure, had been moved closer toward the center and the quota for the next session at the ovarium had been cut.

Wenda found Rio's conversational level of thinking shallow, as though most of his mind had drawn inward contemplatively.

Are you afraid? she thought at him.

Because I come out here to think? He hesitated a little, then said, “Yes, I am. It's the Race's last chance. If I fail-”

Are you afraid for yourself?

He looked at her in astonishment and Wenda's thought stream fluttered with shame at her indecency.

She said, “I wish I were going instead.”

Roi said, “Do you think you can do a better job?”

“Oh, no. But if I were to fail and-and never come back, it would be a smaller loss to the Race.”

“The loss is all the same,” he said stolidly, “whether it's you or I. The loss is Racial existence.”

Racial existence at the moment was in the background of Wenda's mind, if anywhere. She sighed. “The trip is such a long one.”

“How long?” he asked with a smile. “Do you know?”

She hesitated. She dared not appear stupid to him.

She said primly, “The common talk is that it is to the First Level.”

When Wenda had been little and the heated corridors had extended further out of the city, she had wandered out, exploring as youngsters will. One day, a long distance out, where the chill in the air nipped at her, she came to a hall that slanted upward but was blocked almost instantly by a tremendous plug, wedged tightly from top to bottom and side to side.

On the other side and upward, she had learned a long time later, lay the Seventy-ninth Level; above that the Seventy-eighth and so on.

“We're going past the First Level, Wenda.”

“But there's nothing past the First Level.”

“You're right. Nothing. All the solid matter of the planet comes to an end.”

“But how can there be anything that's nothing? You mean air?”

“No, I mean nothing. Vacuum. You know what vacuum is, don't you?”

“Yes. But vacuums have to be pumped and kept airtight.”

“That's good for Maintenance. Still, past the First Level is just an indefinite amount of vacuum stretching everywhere.”

Wenda thought awhile. She said “Has anyone ever been there?”

“Of course not. But we have the records.”

“Maybe the records are wrong.”

“They can't be. Do you know how much space I'm going to cross?”

Wenda's thought stream indicated an overwhelming negative.

Roi said, “You know the speed of light, I suppose.”

“Of course,” she replied readily. It was a universal constant infants knew it. “One thousand nine hundred and fifty-four times the length of the cavern and back in one second.”

“Right,” said Roi, “but if light were to travel along the distance I'm to cross it would take it ten years.”

Wenda said, “You're making fun of me. You're trying to frighten me.”

“Why should it frighten you?” He rose. “But I've been moping here long enough-”

For a moment, one of his six grasping limbs rested lightly in one of hers, with an objective, impassive friendship. An irrational impulse urged Wenda to seize it tightly, prevent him from leaving.

She panicked for a moment in fear that he might probe her mind past the conversational level, that he might sicken and never face her again, that he might even report her for treatment Then she relaxed. Roi was normal, not sick like herself. He would never dream of penetrating a friend's mind any deeper than the conversational level, whatever the provocation.