In the snowy mountains, on a boundary stone between Germany and Austria, lies a strangely staged corpse. Both countries send investigators: the young Ellie Stocker from Berchtesgaden and Gedeon Winter from the Salzburg Kripo. Highly motivated, Stocker takes on her first big case, while Winter, a disillusioned cynic, would prefer to shift the investigation entirely to his German colleague. Interpersonal tensions are inevitable but the two must cooperate because there are more murders and they bear the same signature. It quickly becomes clear that a serial killer is at work. After the description of a surviving victim, a phantom drawing of the perpetrator is created. It shows the devilish grimace of a Krampus, one of those fearsome companions of Saint Nicholas who punish naughty children. Could the killer be on a mission?

The hunt for the "Krampuskiller" has left its mark on the psyche of detective Ellie Stocker and her Austrian colleague Gedeon Winter is in a coma. When a young tourist is found dead near Salzburg, German and Austrian criminal police have to work together again. The ambitious young civil servant Yela Antic is allowed to prove her skills for the first time as a liaison officer in the case of the German Tonia Roth, who was murdered in Austria. The body was found in the Zill valley near a river and the murder has distinctive features. Meanwhile, Ellie Stocker has to take a forced break because she's been struggling with flashbacks since the "Krampuskiller" case. Only when another young woman is murdered does she meet Gedeon again.

After Ellie Stocker and Gedeon Winter become bitter opponents at the end of the second season, events bring them together one last time. A series of mysterious murders on both sides of the border rocks the region. While a crime pattern became apparent in the case of the Krampus murderer and Alexander Gössen, the motives for this series of murders initially remain in the dark for the investigators. The case pushes Ellie and Gedeon to their limits and confronts them with their own story. Because while Gedeon is looking for the tormentor from his childhood, Elli tries against all odds to convict Gedeon of corruption in order to bring the truth about the murder of her colleague Yela Antic to light.