Spirit Walker by Michelle Paver

A cry echoed through the Forest. He froze. It was not the yowl of a vixen, or a lynx seeking a mate. It was a man. Or something that had once been a man. With a creeping sense of dread, Torak watched the light between the trees begin to fail. . . . Torak is a boy apart. A boy who can talk to wolves. A boy who must vanquish the Soul-Eaters . . . or die trying. As the Moon of No Dark waxes large, the clans fall prey to a horrifying sickness. Fear stalks the Forest. The very breath of spring seems poisoned. No one knows the cause and only Torak can find the cure. His quest takes him across the sea to the mysterious islands of the Seal Clan. Here Torak battles an unseen menace and uncovers a betrayal that will change his life forever. Spirit Walker is a spellbinding story of fellowship, treachery, and self-sacrifice that takes the reader further on the journey that began in Wolf Brother.