For twenty years, jewelry thefts have been committed by the same gang, which Maigret has tried to unmask. The leader--he knows it without being able to prove it--is Manuel Palmari, a police informer in his spare time (which has also caused him to lose both legs following a settling of scores). Aline, his mistress, constitutes his only contact with the outside world, and she is closely watched by Maigret. However, despite this surveillance, Palmari is murdered. For Maigret, this crime offers a long-awaited opportunity to shed light on--and determine responsibility for--these infamous and unsolved jewelry thefts.