Murder on Monday: Photo model Monika Stange is found murdered in her apartment in a major West German city. Detectives Bentheim and Laube find rough diamonds hidden in the apartment. The trail leads to a racketeering ring and the influential industrialist Dr. Vogelsang. The latter is not prepared to get involved in the murder case under any circumstances and refuses to testify. Inspector Laube tries to solve the case without his colleague.