Sascha Bergmann from LKA Graz and his colleague Anni Sulmtaler are investigating a suspicious death in Mursbruck.

A man is murdered on a remote riverbank, and a young woman confesses to the murder to the police that same night. Forensic psychologist Karla Eckhardt identifies the confessed perpetrator as Anna Lobrecht, whom she had classified as a compulsive liar in a report two years ago. It's possible that Lobrecht isn't telling the whole truth this time either.

Alexander grows up in a small house with his loving grandmother. In order to avoid his father’s fate, on his tenth birthday, he promises her that he will never fall in love. Every Sunday, Alexander visits his father, who has retreated to live in the Vienna subway system since the death of Alexander’s mother. As a young adult, Alexander wants to be closer to his father and decides to take a job in a lost-and-found office in the underground. It is here that he meets the beautiful and vivacious Caro (Verena Altenberger) in her cute subway hatter store. Although Alexander has successfully resisted love before, now his self-imposed oath becomes a difficult promise to keep.