Commissioner Maigret returns to Saint-Fiacre, the village he grew up in, where his father had been estate manager for the family owning the château.

Early next morning the countess goes to mass at the village church where, on returning to her pew after receiving the sacrament, she falls dead.

Now convinced of a plot to rob and kill the countess, whose young favourite he had once been, Maigret starts his own investigation of what caused her sudden death and who wanted her dead.

Without revealing his hand, Maurice has also been investigating and, while his mother's body is still lying upstairs, organises a macabre dinner party for those he suspects.

At it, Maigret accuses both the doctor and the assistant of negligence, but not homicide, and then reveals that the plotters were the manager and his son, who sought to cut out Maurice and enrich themselves.