The visitor - K.A. Applegate (Animorphs #2)

We can’t tell you who we are. Or where we live. It’s too risky, and we’ve got to be careful.
Really careful.

The thing you should know is that everyone is in really big trouble. Yeah. Even you.

What would you think if someone told you that Earth was under a silent attack? And that the only people who could defend us all were five kids? Well, it’s all true…

Rachel and her friends have been given the power to morph into any animal they touch. So when Rachel starts to suspect that one of her school friends has fallen into the control of the evil Yeerks, she knows just the way to find out the truth…