The Ghostfaces (Brotherband Book 6) - John Flanagan - Bog

When the Brotherband crew are caught in a storm at sea, they're blown far off course and wash up on the shores of a land so far west that Hal can't recognize it from any of his maps. Eerily, the locals are nowhere in sight, yet the Herons have a creeping feeling they are being watched. Suddenly a massive bear appears, advancing on two children.