Chief Superintendent Philippe Maigret - the most decorated police officer in Paris - has been given an undercover assignment by his friend, Christophe Saint-Valry, the Minister of Police. He is to find an ancient grimoire - an 18th Century book about witchcraft - stolen from the Aix-en-Provence reference library some months ago.
What a waste of the man's talent and courage, we might think. But that would be wrong! Someone is using the grimoire for a specific purpose, and animals are being killed in weird ways. How long before the perpetrator takes an even bigger step?
Maigret and his English wife Meg have barely left Paris when they make a gruesome discovery, or rather their cat does, which changes everything: he must cooperate with the Gendarmerie: they are in their territory now. And that seriously upsets his professional balance. Is a month in a lovely cottage in Provence during springtime - all expenses paid - really worth this amount of drama?
However, more is to come. Shortly after they settle themselves in Merion, a quaint little village, Meg makes a further discovery during Philippe's absence. And that really sets the cat amongst the pigeons!