Dvali reached down and scooped a handful of dirt. "What do I have in my hand?"

"Topsoil. Old leaves. Probably a few bugs."

"Topsoil, mineral residue, silts, decaying biomass broken down to elemental nutrients, feeding itself back to itself. Bacteria, fungal spores—and no doubt some insects." He brushed it away. "Much like Earth, but subtly different in the details. On the geological level the resemblance between the two planets is even more obvious. Granite is granite, schist is schist, but they exist here in different proportions. There's less vulcanism here than on Earth. The continental plates drift and erode at a different speed, the thermocline between the equator and the poles is less steep. But what's really distinctive about this world is how fundamentally similar it is to Earth."

"Because the Hypotheticals built this planet for us."

"Maybe not for us, exactly, but yes, they built it, or at least modified it, and that turns our study of this world into a whole new discipline—not just biology or geology but a kind of planetary archaeology. This world was profoundly influenced by the Hypotheticals long before modern human beings evolved, millions of years before the Spin, millions of years before the Arch was put in place. That tells us something about their methods and their extraordinary capacity for very long-term planning. It may also tell us something about their ultimate goals, if we ask the right question. That was the context in which your father worked. He never lost sight of that larger truth, never ceased to marvel at it."

"Planet as artifact," Lise said.

"The book he was writing." Dvali nodded. "Have you read it?"

"All I've seen of it is the introduction." And a few notes, salvaged from one of her mother's convulsive fits of radical housecleaning.

"I wish there had been more. It would have been an important work."

"Is that what you talked about with him?"

"Often enough, yes."

"But not always."

"Obviously, we talked about the Martians and what they might know about the Hypotheticals. He knew I was a Fourth—"

"You told him?"

"I took him into my confidence."

"May I ask why?"

"Because of his obvious interest. Because he was trustworthy. Because he understood the nature of the world." Dvali smiled. "Basically, because I liked him."

"He was okay with that, with your—Fourthness?"

"He was curious about it."

"Did he talk about taking the treatment himself?"

"I won't say he didn't consider it. But he never made the request to me or, so far as I know, anyone else.

He loved his family, Miss Adams—I don't need to tell you that. I was as shocked as anyone else when I heard about his disappearance."

"Did you confide in him about this project of yours, too? About Isaac?"

"When it was in the planning stage, yes, I talked to him about it." Dvali sipped his coffee. "He hated the idea."