In Paris, at the end of the 1950s. Paul Duméry, a former insurer approaching his forties, does not look like much. He survives from day to day, as best he can in a desperate financial situation. Finally, he agrees to meet Sarrebry, a lender-usurer introduced to him by his friend Daubelle. The day before the meeting, Paul's imagination begins to gallop. He sets himself a challenge: to go to the Sarrebry office with a hammer in his pocket. He never stole anything, so commit a crime, no danger. The next day, however, he mortally knocks the antipathetic crook and steals a large sum of money from him. Paul is now an assassin on the loose.