Strollers find a woman's head on the banks of the Rhine in Constance. Shortly after, a female torso is discovered, but it does not belong to the same woman. The people in the lake region fall into a panic: Is a serial killer on the loose? When the girlfriend of investigating commissioner Sito goes missing, the case takes on an even more threatening dimension. Is Sito capable of confronting this perpetrator, who always seems to be one step ahead of him?.