Morphing Hurts: Applegate, K. A. (1996). Animorphs: The Invasion. New York, Scholastic.
A fairly typical story in which a bunch of kids get gifted powers from aliens in order to fight other aliens they are told are evil. But this is Applegate so first, we get to see the second bunch being evil (taking over brains), and second, the people they set out to rescue die, the elder brother of the primary character dies, and at the end one of the kids gets stuck as a hawk. His home life is shit and he quite likes being a hawk, but even so.... not quite what you expect at the end of a cutesy humans with the power of animals story,