Norbert Ritter and Tanja Eck, both married, have a relationship. One day they are found poisoned in the kitchen of the house where they had their dates. Hence there are two obvious suspects: Tanja Eck's husband Stefan and Norbert Ritter's wife Iris. Whereas Iris Ritter claims not to have known anything about the relationship, Norbert Ritter says that he knew his wife committed adultery and he had this information from Iris Ritter. A witness, Martha Koch, testifies that she saw a person, dressed in black, entering the house one day before the victims were found. But it's doubtful whether one can believe her. Kommissar Pauli and his assistant Fischer try to solve this difficult case.