He released her; she sank like a stone. Through the ice-clear water, Wolgast could see that she’d stopped moving; her eyes were open and looking around, like an animal examining some new habitat. Then, with a startling grace, she extended her arms and brought them around, turning her shoulders and pushing herself through the water in a deft, froglike motion. A perfect whip kick: in an instant she was gliding along the sandy bottom, gone. Wolgast was about to dive in after her when she emerged ten feet away, in water that reached well over her head, smiling with exhilaration.

“Easy,” she said, treading with her legs. “Like flying.”

Wolgast, dumbfounded, could only laugh. “Be careful—” he said, but before he could finish she’d filled her lungs with a gulp of air and dived down again.

He washed her hair, did his best telling her how to do the rest. By the time they were done, the sky had darkened from purple to black. Stars by the hundreds, their flickering light doubled in the lake’s still surface; no sounds at all except for their own voices and the basal throb of the lake’s water against the shoreline. He led them up the path with the beam of his flashlight. They ate a dinner of soup and crackers in the kitchen, and afterward, he took her upstairs to her room. He knew she would be awake for hours; the night was her domain now, as it was becoming his own as well. Sometimes he’d sit up half the night, reading to her.

“Thank you,” Amy said as he was settling down with a book: Anne of Green Gables.

“What for?”

“For teaching me to swim.”

“It looked like you already knew. Somebody must have showed you.”

She considered this claim with a puzzled expression. “I don’t think so,” she said.

He didn’t know what to make of any of it. So much of Amy was a mystery. She seemed well—better than well, in fact. Whatever had happened to her at the compound, whatever the virus was, she appeared to have weathered it; and yet the business with the light was strange. And other things: why, for instance, did Amy’s hair not seem to grow? Wolgast’s hair now curled below his collar; and yet Amy, as he looked at her, appeared exactly the same. He’d never trimmed her fingernails either, nor seen her do this. And of course the deeper mysteries: What had killed Doyle and everyone else in Colorado? How could that have been both Carter and not Carter on the hood of the car? What had Lacey meant when she’d said to him that Amy was his, that he’d know what to do? It seemed so; he had known what to do. And yet he could explain none of this.