William Wisting, a widowed senior detective in the Norwegian coastal town of Larvik, leads a murder investigation in which a body is found in snow underneath a Christmas tree. The clothes on the corpse show that the person killed was an American. An FBI team is immediately flown to Larvik and an international hunt for a serial killer begins.

Meanwhile, William's daughter Line, a journalist, investigates the lonely death of an elderly neighbour for an article. When her twin brother Thomas returns to a usually sleepy Larvik to celebrate Christmas with the family, he finds both William and Line deeply preoccupied with their investigations.