Erin Hunter 
Warriors: The Broken Code #4: Darkness Within 

The #1 nationally bestselling Warriors series continues! Discover more epic adventures in the fourth book in the action-packed Broken Code story arc. Exiled after a battle that left all five Clans devastated, Thunder Clans loyal deputy, Squirrelflight, must bring to light an earth-shattering truth: the identity of the cat ruling Thunder Clan while wearing Bramblestars face.While the fate of his body hangs in the balance, the real Bramblestars spirit has vanished. Even Rootspring is powerless to reach himand with tensions among the Clans at a breaking point, Squirrelflight may not be able to ensure Bramblestar has a body to return to. If he returns at all. Packed with action and intrigue, this sixth Warriors series is the perfect introduction for readers new to the Warriors world, while dedicated fans will be thrilled to discover the new adventures that unfold after the events of A Vision of Shadows.