In a mysterious vault beneath the pile of corpses, the police units discover not only more bones, but also a jar of water with leeches. The seemingly insignificant find awakens the memory of Kai, Maggie's missing brother, in Roland Voit and Maggie Kring. Kai was an extraordinary, mysterious boy. Maggie simply cannot and will not believe that he is no longer alive and now hopes to have found proof of this. She asks Adrian Demko for help. Adrian has been in a wheelchair since a terrible accident in their youth, when an unexploded bomb from the Second World War exploded. He instructs his carer Marek Gorski to accompany Maggie on a trip across the border to Poland. The trail leads them to a mysterious building in the border area - where Maggie is assassinated.

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.

Maggie was right: Kai is alive! The siblings hide together in the abandoned forest hut. Kai's confession that he has many people on his conscience upsets Maggie just as much as his seemingly unimaginable explanation. After an attempted assassination, they are both in constant danger. Maggie turns to Voit - without telling him that her brother is alive or revealing anything about his involvement in the series of crimes. Meanwhile, Voit's colleague Zajak deciphers a mysterious document left behind by the survivor of the pile of corpses before his death. On the Polish side, schoolgirl Ilona makes an eerie discovery. Something is wrong at the secluded boarding school for street children and runaways. Blood donations are compulsory, girls are disappearing and sinister men are coming and going.

SoKo Krewlow is on the hunt for Marek Gorski, who has gone into hiding, but a deadly trap awaits the officers in his trailer. Meanwhile, mysterious men have taken control of the Polish boarding school. Pupil Ilona fears for her life. On the run, she discovers a mysterious prisoner. He promises to help if Ilona frees him. Roland Voit is certain: there must be more than one perpetrator! When Gorski demands money from Demko for his escape, the police team drives to a remote drop-off point. However, Maggie Kring and Voit see through the ruse. A fight for life and death begins with the "Great Hunter", in which Maggie outgrows herself - and makes a fatal decision.