Read more about it:
M is called to the Place des Vosges, where the owner of a serum company, Raymond Couchet, has been found shot to death, seated at his desk. Behind him, the empty safe, unlocked, but unreachable with him in his chair. M wonders if the robbery and murder were two separate crimes. He soon becomes convinced that the answer lies among the residents of the block of apartments. Couchet's former wife, Juliette Martin and her husband live across the square. His girlfriend, Nine Moinard, a sometime dancer, lives in the Hôtel Pigalle, and in the next room lives Couchet's son, Roger Couchet, who leads a wasted existence. Mme Martin comes to M's office, and M visits her home to return a forgotten umbrella, where he discovers that the window overlooks Couchet's office. Both Mme and M. Edgar Martin had been seen scavenging among the rubbish bins the night of the crime. Roger commits suicide, jumping out of his hotel window, and Couchet's will is found, leaving a third of his fortune to his wife, his ex-wife, and his girlfriend. Mme Martin becomes ill, and M's suspicion's focus on the Martins. M. Martin heads for the Belgian border, with M in pursuit, and they return to his apatment for a final confrontation, where it turns out his wife nagged him into robbing the safe while Couchet was away at the toilet, but he forgot his glove on the desk. She went down to the office with a revolver, was caught by Couchet, who threatened to call the police, and she shot him. Her husband, feeling guilty, tossed the money into the Seine, and didn't realize his wife was the murderer till later. His run for Belgium had been to establish her innocence, so that she could inherit. Apprehended, she loses her mind.
Maigret of the Month: December, 2004