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.

A German entrepreneur has been killed in Austria. His secret lover was found comatose on a ski piste late at night, drenched in blood. Evidence links this case to the first murder. Ellie, the optimistic and confident investigator from Bavarian Berchtesgaden and her Austrian counterpart Gedeon, the nihilistic cynic from Salzburg, realise they are dealing with a highly intelligent and cold-blooded killer. His victims seem to be symbols for our modern, anonymous society that deserves to be punished.

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.

The demanding investigation has affected Ellie in a major way. The German policewoman and the Austrian cop bicker and fight constantly. While her positive life views get dulled and stunted, Gedeon's initial indifference changes into an obsession for cracking the case. After one lead brings them to yet another dead end, they have to start again from the top. They dive into case files of unsolved murders over the past years, hoping to find any trace of the serial killer.

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.

When the international press conference on the bomb attack gets interrupted, everybody suspects that something major must have occurred: A man wearing a Krampus mask has been shot during a gunfight with the police. It looks like he's the sought-after Krampus Killer. Neither his superiors nor politicians or press want to believe Gedeon's theory that this must be a copycat riding the real killer's coattails. The general demand for a success after months of fear and mayhem is simply too great.

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.