Inexplicable murders occur: Richard Benke, who was suspected of murdering his wife six months ago but was then let go again, is found murdered. Efraim Kiel and a diplomat are also shot. The perpetrator apparently has inside knowledge of the police, because all victims were involved in murder cases. Alex and Fredrika suspect their colleague Torbjörn and search his house. But then the police officer is shot and seriously injured in the bureau's underground car park. Johanna, who was involved in the murder of her parents and sister, is also killed. The perpetrator apparently wants to ensure justice and order and leaves an inexorable blood trail.