The Secret (Animorphs #9‪)‬

There's something pretty weird going on in the woods behind Cassie's house, the place where Ax and Tobias call home. It seems the Yeerks have figured out one very important fact: Andalites cannot survive without a feeding ground. Visser Three knows the "Andalite bandits" don't feed where he does, so there can only be one other place.Now the Animorphs have to figure out a way to stop a bogus logging operation. Because if Visser Three finds Ax in the woods, nothing will stop him from finding the Animorphs.