Maigret 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.