Miss Nováková reports to Major Tůma from the police about the disappearance of her roommate, the model Zuzana. Shortly afterwards, a film director named Konrád asks Tůma to cooperate on a new cinéma-vérité film describing the story of Zuzana's disappearance. Konrád claims that he does not know where the girl, his lover, is. In fact, he himself helped her hide on a houseboat in order to follow the process of investigation and the reactions to her disappearance "for research purposes". Konrád's experiment soon takes a tragic turn. The houseboat is nowhere to be found and the only people who have seen it - a waiter and the deaf-and-dumb watchman Lebeda - do not know anything. Eventually, the houseboat is found lying on the bottom of the lake. Zuzana is found in it, murdered. The police investigate several suspects. Light is shed on the case only when a pack of playing cards is found picturing Zuzana nude and following another murder - this time of the houseboat's owner, Vávra. After that, Tůma and his colleague Captain Líbal, are able to easily unravel the complicated case. In the beginning, greed brought together Zuzana, the photographer Laufr, Vávra and the former printer Rýdl to produce and sell the erotic cards. When the threat of disclosure appeared, Laufr killed Zuzana and Rýdl killed Vávra without hesitation. Rýdl confesses but Laufr is proven guilty by a silent screen test of Zuzana competing for a role in a film, since from the discussion between Zuzana and Laufr, Lebeda reads the truth from their lips. (Verleiher-Text)