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Tchicaya caught himself angrily. The ability to move across the border at lightspeed didn’t guarantee the power to penetrate the far side at the same rate. For all he knew, he’d just seen nothing more than a variation on Branco’s surface-pinning effect.

He told the Left Hand to scribe another probe.

It couldn’t. The border had retreated.

Retreated how far? The Left Hand couldn’t tell him. How do you measure the distance to a featureless, immaterial plane of light? Once the border had slipped out of range of the particle beam of the stylus, the Left Hand had lost the ability to summon forth any kind of echo. It had scattered a small cloud of electronic fireflies, moving at about ten meters a second, to see when they were extinguished. So far, they all remained intact. It was no use tracking the brightness of the borderlight; each square meter of the border would seem dimmer as it retreated, but that effect was canceled out precisely by the fact that any particular instrument you aimed at it, with some fixed angle of view, would be taking in light from a larger portion of the border the further away it was. And there was no Doppler shift to reveal the velocity of retreat: the far side was being pared away, not pushed away, and the new, gray borderlight was being emitted from a succession of different surfaces, not a single moving source that could act as a clock.

The Left Hand had detected a microscopic lowering of the horizon against the backdrop of stars, which did prove that the Planck worms had corroded the far side into vacuum hundreds of thousands of kilometers away. But the line of sight from the Left Hand to the new horizon still only penetrated twenty or so meters below the surface where the border would normally have been; the growing crater could be as shallow as that limit, or it could be a million times deeper.

Tchicaya waited. The fireflies could still wink out at any moment. The Left Hand’s engines weren’t powerful, and it carried only a small reserve of fuel, but it could adapt to a shift in the border’s velocity of a few meters per second.

After ten minutes, nothing had changed. The fireflies were still visible. The border was outracing them.

That did not mean that there was no hope left. But to move the Left Hand faster than the fireflies, to have any chance at all of catching the border, he would need the shuttle.

He was useless on his own, now. It all came down to three Preservationists, and whether or not the hint of life in the far side had been enough to change their minds.

Tchicaya woke his father with a tug of the hand.

"What is it?" His father squinted at him blearily, but then he smiled and put a finger to his lips. He climbed out of bed and scooped Tchicaya into his arms, then carried him back to his own room.

He put Tchicaya down on the bed and sat beside him.

"You can’t sleep?"

Tchicaya shook his head.

"Why? What’s wrong?"

Tchicaya didn’t need to have the truth coaxed out of him. "I don’t want to get older," he said. "I don’t want to change."

His father laughed. "Nine isn’t old. And nothing’s going to change tomorrow." It was his birthday in a few hour’s time.

"I know."

"Nothing’s going to change for you, for years."

Tchicaya felt a flicker of impatience. "I don’t mean my body. I’m not worried about that."

"What, then?"

"I’m going to live for a long time, aren’t I? Thousands of years?"

"Yes." His father reached down and stroked Tchicaya’s forehead. "You’re not worried about death? You know what it would take to kill a person. You’ll outlive the stars, if you want to."

Tchicaya said, "I know. But if I do…how will I know that I’m still me?"

He struggled to explain. He still felt he was the same person as he’d been when he was seven or eight, but he knew that the creature of his earliest momeries, of three or four, had been transformed inside his skin. That was all right, because an infant was a kind of half-made person who needed to be absorbed into something larger. He could even accept that in ten year’s time, some of his own feelings and attitudes would be different. "But it won’t stop, will it? It won’t ever stop."

"No," his father agreed.

"Then how will I know I’m changing in the right way? How will I know I haven’t turned into someone else?" Tchicaya shuddered. He felt less dread now that he wasn’t alone, but his father’s mere presence couldn’t banish this fear entirely, the way it had banished the terrors of his childhood. If a stranger could displace him, step by step over ten thousand years, the same thing would be happening to everyone. No one around him would be able to help, because they’d all be usurped in exactly the same way.

His father conjured up a globe of the planet and held it toward him, a luminous apparition painted over the gray shadows of the room. "Where are you, right now?"

Tchicaya turned the globe slightly with a gesture, then pointed to their town, Baake.