In the Alps, on the German-Austrian border, a bizarrely staged body is found. German detective Ellie Stocker and Austrian investigator Gedeon Winter are called in to investigate.

Another murder of an entrepreneur proves to be very similar to the first case. A drawing of the suspect reveals a devilish grin, and a mysterious message of the `red season' is found.

While looking for a missing woman, Stocker and Winter target a cult that resides in the woods. However, they are not prepared for the next murder.

Stocker and Winter devise a trap for the killer that requires them to go outside the law. However, the killer is always one step ahead, pushing them to play by his rules.

As the trail of the suspect runs cold, Ellie and Gedeon desperately search for more clues, unaware of the murderer's larger plans.

The killer lands another heavy blow, which takes the detectives by surprise. Later, Ellie is targeted by the killer as revenge for her public comment about him.