Two anglers discover a pile of corpses in a field near the polish border. The unimaginably high number of skeletons and animal carcasses leads the police to suspect a serial killer who has apparently been killing undetected for decades. Local detective inspector Roland Voit is assigned to support the large LKA contingent in the Oderbruch. His former childhood sweetheart, former policewoman Maggie Kring, is also called to her home town of Krewlow. After years of silence, Maggie and Roland are anything but impartial. Maggie is following her own investigations. She left Krewlow in 1997 after her brother became a victim of the historic Oder flood at the age of 17. The ex-policewoman doubts everything she knows - including the death of her brother Kai.

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 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.

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.

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.

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.