The Place of No Stars (Warriors – Broken Code #5) by Erin Hunter
The time has come to return to the Dark Forest.
ThunderClan’s deputy, Squirreflight, has vanished with the cat now known to be an impostor, sowing suspicion and mistrust among the five Clans. The cause of their ancestors’ silence is finally clear—but so is the terrifying truth of the danger they must face if they hope to bring light back to the darkness. . . .