Maigret is in Les Sables-d'Olonne, on vacation with Mrs. Maigret, but since the second day she's been in the hospital, recovering from an operation for acute appendicitis. Maigret has settled into a pleasant routine, touring the cafés at regular times, visiting his wife, watching a bridge game at the Brasserie de Remblai. He'd received an odd note about a patient at the hospital, apparently from one of the sisters, but before he'd had a chance to think about it, he learned that the patient had died.
She was Lili Godreau, the 19-year-old sister-in-law of Dr. Philippe Bellamy, an eminent neurologist, who happened to be one of the bridge players Maigret watched every day. She'd fallen out of his car as he was bringing her back from a concert in La Roche-sur-Yon, and hit her head. Bellamy struck up Maigret's acquaintance and brought him back to his house, where, as they entered, a young girl dashed out. Maigret had the feeling Bellamy was troubled by the incident, and spent most of his evening trying to identify and locate the girl.. Bellamy's wife, Odette Bellamy, Lili's sister, had been ill for the past few days, and didn't leave her room.
The next morning the local chief of police, Mansuy calls him to report that they'd located the girl, Lucile Duffieux — she'd been strangled during the night. From there on it is a contest with Bellamy, for Maigret is sure of his guilt. He learns that Lucile's brother, Émile Duffieux, has apparently left town for Paris, sending letters to his mother and boss at the local paper, but no one had seen him leave, or since. Maigret returns to the hospital and interviews the sister who'd passed him the note, and learns that Lili had spoken in delerium of a silver knife, and that "he wasn't guilty...".
Maigret is convinced that at least one more person is in grave danger, and spends the next morning searching the area for somewhere that Odette, of whom he is known to be obsessively jealous, had gone frequently. He finally locates Olga's, a dressmaker, and asks her if it wasn't true that Odette and Émile had secretly met there, and planned to run away together, and she admits it. At that moment Bellamy calls him, and he goes to his house, where he admits all. He'd discovered Émile's letters to his wife and their plans. He'd sedated his wife, met Émile and killed him, hiding his body in an abandoned cistern. Lucile had brought their notes back and forth.
This report prepared by Dana Samson