A cleaning lady finds Dr. Scholz dead in his practice. The cause of death is quickly determined: a poisoned yogurt from the local dairy in Niebüll. During his investigation, Commissioner Thamsen learns that the dairy is being blackmailed. But who is behind the threats and the poisoning? The son of the dairy owner and several members of an activist group come under police scrutiny. However, none of the investigative leads lead to a solution of the case, and the pressure mounts rapidly when there is another victim.