An alarm sounds in the middle of the night for a burglary in progress at a winter-closed campsite in Bredäng, outside Stockholm. The nearest police car answers the call. There is a light in one of the farthest caravans and when the officers open the door they are greeted by a horrific sight. Floors, walls and furniture are completely covered in blood. A man has been killed with an axe and brutally dismembered. On the floor of one of the rooms lies a young man sleeping with a severed arm as a pillow. He is arrested and taken to Kronoberg prison, identified as seventeen-year-old Hugo Sand, the son of a famous writer. It turns out that Hugo suffers from an unusual kind of somnambulism that is activated by nightmares. He can either be a perpetrator or a witness, but claims himself that he remembers nothing from the night. Detective Joona Linna, who is connected to the case, contacts her old friend Erik Maria Bark to use hypnosis to try to find out what happened inside the caravan. This becomes the starting point for a complicated hunt for a serial killer who has just entered an extremely active phase.