Germany, the year 1930: With his epic "Nibelungen" movies and the futuristic spectacle "Metropolis", filmmaker Fritz Lang has created instant classics of silent cinema. Now he is eager to make his first sound feature film and starts looking for a suitable story. In contrast to his silent films, he want to tell a contemporary tale rooted in reality. He travels from Berlin to Dusseldorf, where he seeks inspiration from the work of renowned police detective Gennat. Gennat is currently investigating the crimes of notorious serial killer Peter Kürten, also known as the "Vampire of Dusseldorf". Taking cues from the real-life case, Lang begins to construct the story that will eventually become his masterpiece "M – Eine Stadt sucht einen Mörder". Yet while developing the film's story, the director also has to face the dark chasms of his very own soul.