My name is Simon. I’m 10 years old. I’m a serial killer. Robert Stern (Rupert Penry-Jones), a successful defense attorney, doesn’t know what lies in store for him when he agrees to meet a new client in a derelict estate on the outskirts of Berlin. Stern is more than surprised when his old love interest and professional nurse Carina (Emilia Fox) presents him with a ten-year-old boy as his new client: Simon (Jack Boulter), a terminally ill child who is convinced he murdered many men in a previous life.
Robert’s surprise turns into horror when he and Carina find human remains in a cellar the boy has led them to—the remains of a man whose head was split with an axe 15 years ago, just as Simon claimed. Things go from bad to worse within hours: Stern discovers more dead bodies, the investigating police officer Engler (Andy Serkis) begins to chase him as a suspect, and his own past comes back to haunt him. Stern’s friend and former criminal Andi Borchert (Stephen Marcus) is the only one to believe Stern and Carina. Hunted by the police and led by Simon’s memories, they begin to investigate Berlin’s shady subcultures and soon discover horrors more gruesome than anything they could have imagined.