Spirit Walker: Michelle Paver

Thousands of years ago an orphan boy and his wolf cub companion challenge a demon bear that threatens to destroy their world forever. With the help of the World Spirit, Torak destroys the bear, but his beloved Wolf is lost in the ensuing avalanche.
And Torak's quest is far from over. A strange, creeping sickness, silent and deadly, is threatening the Ravens. Word arrives that the Seal Clan have the cure and Torak must face a lonely journey to find it. On the Seal's Island he stumbles into a world utterly unlike his own. Here life moves to the rhythms of the sea, the Seals build shelters from whale bones and skim the waves in fast, beautiful kayaks. And here Torak is welcomed by the kindly Seal Mage, Teneris, and kinsman, Bale. But all is not as it seems - Torak must keep his wits about him to judge who might be friend or foe.