Maigret is not at all pleased to become reacquainted with the dubious Leon Florentin, who was at school with him and now needs his help.

While in Brussels where he is being rewarded with the Order of Leopold, Maigret is asked for by a man named Xavier Marton who tells him that he suspects his wife Gisèle to want to murder him. Then the man disappears. The following evening a woman by the name of Gisèle Marton is waiting for him in the lounge when Maigret arrives in this hotel. She warns the French commissaire that he must not believe what her husband has told him as the man is paranoiac. Puzzled by this unusual situation, Maigret decides to investigate. At the Martons'luxurious house (another oddity ...

Dr. Baron is a respectable physician, married with two children. When his servant girl from Brittany dies of poisoning, her parents file a complaint with the police. Maigret travels to the doctor's home in Neuilly and investigates allegations of foul play associated with another servant; he also learns that a vagrant visited the house weekly.

While assisting the police elsewhere in France, Maigret becomes unofficially involved in a missing persons case involving the husband (Marcel Blanc) of a young woman (Germaine Blanc). She's trying very hard to find her husband who has disappeared under mysterious circumstances, but she is very reticent when speaking about it to Maigret. As he follows her and finally gains her partial trust, the plot begins to expand to include stolen paintings, crooked boxing and a fence who turns out to be Germaine's father.

A tramp is found, unconscious and wounded, in the Seine.

When the wealthy owner of a pharmaceutical company is shot and killed at his desk with a plundered safe behind him, Maigret wonders if it was just a robbery gone wrong. Whatever it was, he's convinced the answer lies down the block, where the victim's ex-wife and her husband, his girlfriend and his wastrel son all live.