She crawled along the accessible perimeter of the room for the second time, feeling with her hands for anything hopeful—a draft or some promisingly loose heap of rubble. And for the second time found none.

She had begun to believe she might die in this awful place on this awful planet, haunted by the ghost of Esh. Haunted, that is to say, by the Hypotheticals.

In whom she did not believe, at least not in the sense Avram Dvali believed in them. The Hypotheticals were a network of self-replicating spaceborne machines. Some long-extinct civilization must once have seeded its local environment with these devices, or perhaps it had happened more than once, a multiple genesis over many millions of years. Either way, once variable self-replication was introduced into the medium of interplanetary and interstellar space the process of evolution was engaged—different from organic evolution in every detail, but not in principle. Like organic evolution, the process had generated strange and gaudy complexities. Even such apparently "engineered" devices as the Spin barrier that surrounded the Earth, or the Arches that linked planets separated by vast distances, were ultimately no more intrinsically intelligent than such biological constructions as a coral reef or a termite hill.

The periodicity of the ashfall and the truncated grotesqueries it generated were proof enough, she thought. What had been installed in Esh—and in Isaac—was nothing more than a tragic susceptibility to alien tropisms. Esh could not be a "communicant" because there was no one with whom to communicate.

Evolution did, demonstrably, produce minds, and she supposed it was possible that the long interstellar evolution of the Hypothetical machines had also produced minds—locally, temporarily. But such minds, if they existed, were the byproduct, not the process. They controlled nothing but themselves. They couldn't be "the Hypotheticals" as Dr. Dvali imagined them to be.

She remained unnerved, however, by the obvious fact that Isaac remembered Esh, who had died many years before Isaac was born. If Esh had become a memory in the networked ecology of the Hypotheticals, could such a memory possess volition? And who or what was the rememberer?

"Sulean—"

This was Mrs. Rebka, who wouldn't leave Isaac's side. Her voice came out of the darkness of their sealed tomb as if from an infinite distance. "Yes, what?"

"Do you hear that?"

Sulean hushed her own thoughts and listened.

An intermittent scraping. The tack-tack-tack of something solid tapping stone. Followed by more tentative scraping.

"Someone's trying to dig us out," Mrs. Rebka said. "It must be Avram and the others, they must know we're here!"

Tick-scratch-tick. Yes, maybe, Sulean thought. But then Isaac said, very suddenly and with startling clarity, "No, Mrs. Rebka. It isn't the other people who want in. It isn't people at all. It's them."

Sulean turned toward the place from which Isaac's voice had come. She quelled her own fear and said,

"Isaac, do you really know what's happening?"

"Yes." His tone was unexcited. "I can see them."