The wife of Albert Constantin goes to visit her uncle, who is sick. Albert, (Fernandel), a clarinet player with the orchestra of the Théâtre du Châtelet finds himself alone for a week. Albert finds it hard to cope, being domestically inept, and his colleague in the orchestra, Émile, (Jean Rigaux), recommends he go to see Éva (Judith Magre). He, himself, sees her from time to time. At first hesitant, Albert goes to see the woman.
So much the worse for Albert. Éva is murdered, while he waits to see her in her living-room. Realising Éva is a prostitute he hurries away, only to read the next day of a murder and reports of a man running away, in a raincoat, from the scene of the crime. He soon finds himself dealing with a blackmailer, a neighbour of the murdered woman, Monsieur Raphaël (Bernard Blier), and professional killers. And so Albert is overtaken by a series of events that plunge him ever deeper into troubles.
