One day, Maigret visits Jean Lenoir, a criminal, in his cell to tell him that his reprieve was not granted. Lenoir starts to talk about something very different, how one day someone dumped a body in canal Saint-Martin and how he and his friend Victor had seen him and blackmailed him. In time, he lost track of him but he run into him once at the inn Guinguette a Deux Sous. Some time later, when Maigret is buying a hat, he overhears a man planning to go to that inn and follows him. The man's name was Marcel Basso. A few days later the Inspector finds out that this Marcel Basso killed a man called Feinstein.
Feinstein's wife, Mado, was Basso's mistress and when Feinnstein had tried to get money from Basso and threatened to kill himself if he could not they struggled for the gun and Feistein was killed. Basso was arrested but he escaped.
At the Taverne Royale, Maigret makes a new drinking partner, James who works in an English bank in Place Vendome. He returns to the inn even if he promised Madame Maigret to go to Alsace. There he encounters a man called Victor Gaillard in who Maigret recognizes Jean Lenoir's partner. But Victor does not want to say who the murderer they once blackmailed was. Basso was arrested again while trying to run away with his wife and children and he puts him in Victor's cell.
Now, the inspector has two dilemmas: why did his drinking partner, James tried to help Basso to flee and who was the mysterious murderer and why did the two partners protect his identity?
This report prepared by Dana Samson