Poland, summer 1990: ten-year-old Kai has been taken to safety by his mother Minna to stay with Polish friends. His father Arthur wants to kill him because he suspects that Kai has a sinister tendency. His sister Maggie fearlessly stands up for Kai and has to protect him from other children. A fight breaks out on the way to school, in which the leader Conradi is seriously injured and Maggie is knocked unconscious. Kai swears to his father that he will never tell Maggie the truth about himself. A sinister man also knows that the introverted boy is special. He seeks Kai out and offers him the chance to live with his "real" family.

Kai can't live with his guilt and wants to shoot himself. Maggie saves him at the last second. She wants to give her brother the chance to work together to find the people behind the unimaginable crimes and make amends. In order to stop the series of crimes, the ex-policewoman sets out in search of the key figure: the "Great Hunter". A trail leads back to 1947, when two men came under suspicion of having committed gruesome murders. One of the suspects was Maggie's now 90-year-old father Arthur, the other disappeared a long time ago. Together with Roland, Maggie uncovers a disturbing family secret.