M travels to the tiny town of Saint-Aubin-les-Marais, near Niort, in the Vendée, at the request of the Examining Magistrate Victor Bréjon. His brother-in-law, Étienne Naud had asked him for help, since after the death of a young man, Albert Retailleau, rumors had been flying that Naud was involved. M is surprised to see Old Cadaver, Justin Cavre, who'd been on the force with M for 20 years till forced to resign due to problems caused by his wife. But Cavre, who also goes to Saint Aubin, ignores him. M quickly learns that no one in town wants to help, except one young man, Louis Fillou, who'd been Albert's friend. M learns that Albert had been the lover of Geneviève Naud, and had gone to see her the night he was killed. But that night he'd been angry, and told Louis it was all over. M is surprised when Alban Groult-Cotelle, a friend and frequent house guest at the Naud's, appears at the Naud's house with a hotel receipt, showing his "alibi" for the night of the crime. M begins to understand, watching Geneviève's face, and accompanies Alban home, where he finds Cavre. Naud calls his brother-in-law to have him call off M, but before leaving M summons all together at Naud's. Alban, in his 40s, had been having an affair with young Geneviève. When she became pregnant, he'd had her take up with Albert, to claim he was the father. Naud had seen him leave her room by the window the night he had argued with her, and killed him in a rage. Albert had learned of the deception. After that, with Cavre's help, they'd paid off everyone to forget about it. M left it that way, and learned that two years later, after the Naud's had moved to Argentina, Alban had married Geneviève.