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.

Wisting's team continue to search the bottom of wells all over town for more gruesome clues. They realise that the killer could also have been operating across the border in Sweden, potentially multiplying the number of victims.

Line's investigation is also becoming more complex, meaning Thomas has his work cut out trying to unite the family at Christmas.