The war of the ember / Lasky, Kathryn

After a malignant power is summoned, the six owl kingdoms prepares for war, and while the Guardians of the the Great Ga'Hoole Tree call together an army of gadfeathers, kraals, polar bears, green owls, puffins, seagulls, and dire wolves, another army of free creatures travels to the Hot Gates of Beyond.

Unbeknownst to the Guardians, in a long-empty cave two ruthless villains join forces to conjure an ancient evil, an evil that will do their bidding and wreak havoc on the world.