The Visitor by Chris Grine is an adaptation of the second Animorphs book by K.A.Applegate. The Animorphs continue to fight against the Yeerks while knowing hardly anything about the invading aliens. Their idea to learn more is to observe Chapman to see if he can give them any more leads. But to do that Rachel must face the true horror of what the Yeerks are doing.
I tend to have Mini-Reviews be spoiler free. But as this is an adaptation, I am not going to hold onto that rule like usual. So if you don't want spoilers for the graphic novel adaptation or the original book, I suggest you read those first before continuing.