A frozen body is found on the boundary stone right on the Austro-German border, as if propped up for some pagan ritual. Shortly after the disparate investigation duo, police inspector Gedeon Winter from Austria and commissioner Ellie Stocker from Germany, have joined up on the case. The killer has sent audio messages to the press. The unsettling recording from the victim taken before her death, as well as intricate elements of the crime, make the investigators suspect this murder is merely the beginning of a greater scheme.

Tipped off by the killer's horrific photofit, the investigators unearth the Krampus legend - a symbolic creature infamous for punishing the naughty and unworthy. This leads them to Sebastian Brunner, head of a rural sect, whose books on the end of civilisation seem to have inspired the killer. Through the cult leader, Ellie and Gedeon manage to contact the perpetrator via the internet. This achievement, however, can't stop the murder of a YouTube starlet on a lake near Salzburg.

In a joint effort with cultist Brunner, Ellie and Gedeon try to set a trap for the killer. For this plan to work, they have to overstep legal boundaries. Trying to gain the trust of the killer, they feign a copycat murder, hoping their target would be lured into reaching out to Brunner. Meanwhile, Ellie has started an affair with her superior, whereas Gedeon has been haunted by his shady past as a corrupt narcotics cop.

A fierce detonation blows up a fashion outlet mall in Salzburg. Despite Ellie and Gedeon trying to evacuate the building in time, a child is fatally wounded in the explosion. The deadly assault riles up the general public, whereas politicians and the media demand fast results from the police. In Austria, Gedeon has to fight to stay on the case. In Germany, Ellie loses trust in her superiors more and more. After the Krampus Killer has leaked details of her affair with her boss to the press, her life collapses.

In the Austrian region Steiermark, a decayed female body is found in a buried wooden box. When the victim is identified as Malica, Gedeon senses the Krampus Killer has struck again. At first, nobody shares his suspicion. But his reinvigorated eagerness convinces Ellie to pick up an unofficial investigation on their own. They find out that the Macedonian victim, Malica, has been reported missing back home.

Gedeon wakes from a coma only to receive unwelcome news from his medical team. Meanwhile, Ellie struggles to hide the extent of her trauma. A new case comes in from Austrian investigators—prompting Ellie to pass it to new colleague Yela.