Taxi driver Koukal () is stopped by the police for a routine traffic check. In the boot of his car the police find the body of a naked man. Koukal is arrested even though he claims he knows nothing about it. The case is assigned to Major Mlynár (). The police identify the corpse as that of an Austrian citizen called Mitrik. Koukal has been regularly driving people interested in gambling to a secret gaming den. The police are put onto the gambling den by another taxi driver, who admits that he drove Mitrik there. Mlynár and officer cadet Pecka () feign interest in gambling and visit the gaming den incognito.