In a suburban villa, a woman of means is murdered. Police Superintendent Zdychynec from the Prague Liben neighborhood reports the case to Police Councilman Vacátko, upon whose order an investigation is launched immediately. Zdychynec begins to suspect the wooer of his own daughter, a handsome dragoon named Rudi, of the crime. In Rudi's absence, Zdychynec searches his rented room in the apartment of the elegant Mrs Dragicová. All his findings - among others, sand left on Rudi's jackboots and a decent amount of money in his bedside table - convince the superintendent that he is following the right lead, especially when Rudi refuses to say where he was at the time of the murder.