Normally at home in Canada's Arctic Circle, 15-year-old Nick Thrasher kills a caribou, but then loses the meat to a fearsome creature he has never met before: a 900-pound "grolar" bear — half grizzly, half polar. Out of the blue, Nick's half-brother Ryan, now a famous wildlife photographer, contacts Nick. He wants to raft together down the remote Firth River and take some pictures of caribou. Nick agrees, but before they get too far disaster strikes and the two end up in the freezing river. Can Nick and Ryan survive the wilderness and each other while the grolar bear remains on the loose?