When a disembodied arm that turns up in the Canal St. Martin is noted to be that of a man, Maigret is called in to take charge of the investigation.  A search for a phone leads him by chance to a small, dark bistro where he becomes fascinated with the proprietress, Mme Calas.  One thing leads to another, as they always do with Maigret, who is more fascinated with Mme. Calas and her story than he is with the body parts which are missing the head.  Turns out that Mme. Calas is the estranged daughter of a wealthy brute from the countryside who married another peasant brute as revenge and when she is identified as the heiress to a fortune, her real love murders the brutish and abusive husband.  All quite a long way around to examining the psychology of the venegeful child, but Maigret does solve the murder and continues on his way.  Maigret muses in one scene how he is really a guide and a psychiatrist more than a detective, helping people figure out their complicated and messy lives.   Another satisfying Simenon for a winter’s night.