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.
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.
