The Visitor: the Graphic Novel (Animorphs #2)

Rachel is still reeling from the news that Earth is secretly under attack by parasitic aliens, the Yeerks. Now she and her friends are the planet's only defence-five kids who, purely by chance, stumbled onto a downed spacecraft and were given the power to morph into any animals they touch. Rachel's fearless. But what she finds inside may be more than even she can handle.