Katrín Gunnarsdóttir is an ambitious investigating police officer with an eye on the position of head of the research department. When an elderly man is found murdered at Reykjavik harbor under unusual circumstances and Katrin is called on the scene, a scenario she has little control over begins.

Arnar Böðvarsson has been brought to the country to help the Reykjavik police in the investigation of the murders, as it is suspected that a serial killer could be on the move. Arnar is a mysterious investigating officer who has lived in Oslo for a long time and his return is stirred up in old memories.

An older woman is found dead in Valhöll's teenage home and seems to have been the same killer. The police have no idea of ​​the reasons for the killings or who is behind them.

When it turns out that Valhall's last employee is still alive, Kata and Arnar fear that the serial killer will find him ahead of them. At the same time, the police delve deeper into the shadowy history of the adolescent home and the boys who were there.

Kata and Arnar finally believe that they have come on track with the serial killer, but the investigation leads them to the paths they least expected. Difficulties in their private life take their toll.