Maigret investigates when an ace safe-cracker stumbles upon the body of a woman and then flees the scene of the crime.

Joseph Gastin is headmaster in the village school at La Rochelle. One of his pupils has supplied enough evidence to have him convicted of murdering the local postmistress. He persuades Maigret to go to La Rochelle and prove him innocent.

Police dismiss the claims of an elderly woman about things being moved in her flat.