Animorphs: The Visitor (Book 2)

There is an invasion. Earth is under attacked. And the only hope we've is a group of kids. 6 kids. 4 normal-looking-but-not-so-normal kids, 1 once-a-kid-but-not-anymore, and 1 alien-cadette kid. Against a whole race called yeerks and the controllers ( 7 feet tall walking razor blade called Hork-bajir, giant hungry c...