“What is that thing?” Isaac said as they came to a halt at an intersection. Up ahead was the wild part of the library, with its random clusters of bookshelves and portal-books.

“I have never heard of its like,” Dex said. She was breathing hard. “The caryatid armor can be broken, but I have never seen it . . . melt.”

A prison, Alice thought. The Infinite Prison. That thing had been inside all along. Someone had trapped it, and hidden it away in the Palace of Glass. And I let it out.

“I’ve never seen a creature disappear that way,” Isaac said. “As if it was absorbing them.”

“It was.” Ashes hopped down from a shelf in a puff of dust. “Alice, are you all right?”

She blinked. “I think so. I feel a little drained.”

“Jen won’t wake up,” Michael said. His voice was calm, but Alice could hear the urgency underneath.

“Drained is about right,” Ashes said. “If it got one of her creatures, it took a lot of her energy along the link. She’ll wake up okay, if we get out of here.”

“How do you suddenly know so much about it?” Isaac said.

“I talked to Mother,” Ashes said. “At no small personal risk, let me tell you, because the fur is flying over there. But that thing . . .” He huddled in on himself, ears flattened, tail sweeping back and forth in the dust. “It’s called the Ouroborean.”

“The Ouroborean?” Alice said. “Like there’s only one of it?”

“Exactly. It’s not a creature, not like you or me or anything on the other side of a portal. It’s more like a living spell, or a walking book. The Readers made it, a long time ago, in the time before the libraries and the labyrinthine. It’s a weapon. And then they had the good sense never to use it, which if you know anything about Readers should already be terrifying.”

“Why wouldn’t they use it?” Michael said. He’d sat down with Jen’s head in his lap.

“Because once it gets started, it can’t be stopped,” the cat said. “It eats magic, uses it to make itself stronger. It’ll devour anything you can throw at it, and anything it finds in the library. It just keeps going and going until there’s nothing left. What’s the point of a weapon that devours all the treasure you were hoping to steal?”

“What’s it doing here?” Isaac said.

“I brought it here,” Alice said, her voice flat and dead. “I went looking for something I shouldn’t have, and I brought it back with me and let it out. This is my fault.”

“No wonder the Readers are so scared,” Isaac said.

“The Most Favored must have known what happened,” Dex said. “She sent us here to lock it back up again.”