In the heart of the dark forests of Sandviken, Sweden, a shocking discovery turns the lives of four families upside down. Connected by fond memories of summer vacations, they are haunted by a long-buried sinister secret. For 30 years, a sadistic serial killer has been living among them, hunting innocent young girls for his twisted pleasure. The investigation is a grueling race against time, and the detectives in charge must confront not only his cunning and ruthless nature, but also their own inner demons.