There was a warning siren in the middle of the night about an advanced break-in at a winter-closed campsite in Brändåk, outside Stockholm. The police discover a light in one of the most remote caravans, and when officers open the door, they face a gruesome scene. Floors, walls, and furniture are completely covered in blood. A man has been killed with an axe and has been brutally decapitated. On the floor, a young man sleeps with a severed hand serving as a pillow. He is arrested and taken to Kroneberg Prison, identified as seventeen-year-old Hugo Sand, the son of a famous author. Hugo suffers from a rare sleepwalking condition triggered by nightmares. He is either the perpetrator or a witness, but claims to remember nothing from that night. Detective Yona Lina contacts his old friend Erik Maria Barch to use hypnosis in an attempt to uncover what happened inside the caravan. Thus begins the sleepless search for a serial killer that has just started . . .