The large LKA contingent is searching for a serial killer in Krewlow and hopes to get a clue from the only survivor found on the pile of corpses. However, the seriously injured man is unresponsive. For the village doctor Frank Seeger, it is clear that "Pulver-Paul" is behind the bloody deeds. The gun-crazy hermit is holed up on his farm and obsessively believes he has to defend himself against overpowering enemies. When Roland Voit and Stanislaw Zajak want to interrogate him, a life-threatening confrontation ensues. Meanwhile, Maggie is staying with Adrian Demko, her childhood friend who is in a wheelchair. She is convinced that the key to the Oderbruch serial murders lies in their shared past.

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 Kring and Kai travel to the Carpathian Mountains. There, the siblings try to find out who the mysterious man is who came to the Oderbruch with their father in 1947 as a former war deserter. In Romania, however, they initially come up against a wall of silence. Roland Voit follows Maggie's tracks, even though he has been suspended from the case. He discovers the body of a dead teenager in the forest hut. When his Polish colleague Stanislaw Zajak tracks him down, Voit has no choice but to play his cards close to his chest. Zajak entrusts him with a theory about similar unsolved and mysterious murders in other countries and forces Voit to help find Kai.