The Absolute (Animorphs #51)

The Yeerks aren't playing around anymore. They're no longer hiding behind a silent invasion. And one of the first steps in their new plan is to take over the National Guard, to prepare for all-out war against humanity.

Marco and the other Animorphs couldn't be less prepared for this news. The Yeerks know who they are, forcing them to hide to protect their families. Things are falling apart, and for once Jake may not be able to make the decision that will save them...