Maigret is visited in his office by Valentine Besson, a lively old widow from Étretat, whose maid, Rose Trochu, has been poisoned — or at least she'd drunk poison that apparently was intended for Valentine. Valentine's step-son, Charles Besson has recently become a Deputy, and the Minister has asked the Chief to send Maigret.
At Étretat Maigret is met by Inspector Castaing, of Le Havre, who was in charge of the case. So far nothing was clear, but Valentine's daughter, Arlette Sudre, had stayed in the house and been visited by a man Hervé Peyrot, who wasn't her husband. Maigret visits Valentine's house, and has a chance to interview Arlette, and so gets some of the background of the family. Arlette and her mother weren't fond of each other. Maigret had also seen Valentine's two step-sons, Charles and Théo Besson, the latter with Henri Trochu, Rose's brother. Maigret takes a trip to Yport to visit Rose's family, and discovers that she had an emerald ring of great value. He returns to Étretat with Henri, who is soon to set to sea, and charges Castaing with keeping an eye on Théo, who he has learned had been seeing Rose. But Théo has left his room without being spotted, so Maigret and Castaing rush to Valentine's, where they find she has shot Henri through the door, assuming he was trying to break in. But Maigret has understood. Rose had found the emerald, and Théo had learned of it from her, confirming his belief that his step-mother still had her real jewels. Valentine had tricked Rose into drinking the poison once she'd learned Théo was seeing her, afraid of what he'd learn. She called Théo to come up to her house, but he'd sent Henri ahead, and he'd gotten shot in his place.
This report prepared by Dana Samson