The War of the Ember (Guardians of Ga'Hoole, #15)

Not an ambush. Not a battle. But the final confrontation: War.

In this last chapter in the great of the Guardians of Ga'Hoole the Striga and Nyra join to conjure a malignant power from hagsmire itself. When news of their alliance reaches the Great Ga'Hoole Tree the Guardians call to good creatures everywhere: gadfeathers, kraals, polar bears, greenowls,puffins, seagulls, and dire wolves. An army of free creatures marches, swims, and flies to the Hot Gates of the Beyond, where the fate of the six owl kingdoms will be decided once and for all.