The movie is based on real events and deals with the background to the shooting of Lang's thriller "M - A City is Looking for a Murderer." It is 1930 and Fritz Lang has been successfully active in the film business for eleven years. He is looking for material for a new film, a sound film. He is tired of the large-scale projects, his next film is said to be significantly smaller. In addition, there is a crisis in his relationship with Thea von Harbou, who seems to be more and more enthusiastic about the ideals of National Socialism. During his research, he comes across reports about a serial killer from Düsseldorf. He travels from Berlin to the Rhineland and joins the crime commissioner Ernst, who heads the investigation. Peter is arrested as a suspect, Fritz is given the opportunity to interview him. When he meets Anna, friend of a victim and suspected eyewitness, he is overwhelmed by memories of his first wife Lisa, who looks immensely similar to Anna, and who shot Peter when she caught him with Thea von Harbou.