Darkness Within (Warriors: The Broken Code, Bk. 4)

Exiled after a battle that left all five Clans devastated, ThunderClan's loyal deputy, Squirrelflight, must bring to light an earth-shattering truth: the identity of the cat ruling ThunderClan while wearing Bramblestar's face. With tensions among the Clans at a breaking point, anther battle looms, and even Squirrelflight may not be able to ensure Bramblestar has a body to return to. If he returns at all.