Police Commissioner Jules Maigret returns to the small village where he spent his childhood at the request of the Countess of Saint-Fiacre, who has received a disturbing anonymous letter.

Bum Archimède wants to spend the winter in prison, but to get there proves not to be that easy.

A doctor at a run-down psychiatric hospital is offered a large sum of money to shelter a new patient. Soon the place is full of suspicious and secretive characters, all apparently international secret agents trying to find out who and what the patient is.