In the middle of the nudist area of the Danube floodplains, a couple is murdered. On the chest of the dead is a bloody mark. Is it a crime of jealousy or a ritual murder? A similar murder a year earlier could never be solved – now the "love couple murderer" has apparently struck again. Stockinger investigates at the scene and finds a suspect, but cannot prove anything to him. Inspector Moser, together with his colleague Elisabeth Böhm, decides to set a trap for the murderer: On the nudist grounds, the two disguise themselves as lovers. Rex hides nearby to warn her in time. A hot night begins...