The Warning (Animorphs, #16)

Jake's made a pretty amazing discovery. It seems like there may be other people who know about the invasion. Others who know about the Yeerks. Jake finds a Web site devoted to the Yeerks. And Jake, the other Animorphs, and Ax aren't sure it's too good to be true.

But if they try to investigate the site and it's a trap, there's no way the Yeerks won't find out who they are. If they don't check it out, they'll never know if they're the only ones fighting. Whatever Jake and the others decide to do, they've got to move quickly, because Visser Three isn't the only one dying to meet them. . . .