SPOILER ALERT!
Sabriel - Garth Nix
""I see you have found that book," he said, tail flicking backwards and forwards as he spoke. "Take care you do not read too much."

"I've already read it all, anyway," replied Sabriel, shortly.

"Perhaps," remarked the cat. "But it isn't always the same book. Like me, it's several things, not one.""