 A masked bandit steals valuables from Commendatore Anzaloni s apartment and flees, leaving Anzaloni unharmed. Inspector Ingravallo is called in. The robbery is suspicious; the thief found the jewellery too quickly. The neighbour, Liliana Banducci, employs a servant girl, Assuntina. Her fiancé, Diomede, tries to flee when he sees police tailing Assuntina. But Diomede has an alibi, a rich American woman... Liliana s cousin, Dr. Valdarena, pays her a visit, only to find her body on the floor. But before calling police, Valdarena removes an envelope addressed to him from the sideboard... Liliana s husband Remo was away from Rome at the time of the murder, but he is surprised to hear that Liliana had changed her will only the week before...