Rook: Exodus (Rook: Exodus #4)

It's all-out war on the planet Exodus! The bear warden Ursaw wants complete control over the world, and he'll destroy anyone and anything in his path. Rook, Dire Wolf, and their newfound allies are the only remaining wardens left to stop him. The question is: What could Ursaw possibly want with a dying planet everyone else is trying to escape?