for The Secret by Katherine Applegate
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 thing: 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.
Publisher description retrieved from Google Books.