The Provence Puzzle, by Vincent McConnor (epub/Kindle/pdf)
The first in the classic series featuring Chief Inspector Damiot of the Paris police.
"Chief Inspector Damiot of the Paris police, recuperating from a bullet wound, seeks sun and rest in Courville, his boyhood village in Provence. But Courville is lately in a ferment about the unsolved murders of two young girls--one a promiscuous villager, the other still unidentified. And there are also rumors of a monster seen at the supposedly-empty Chateau De Mohrt. Intrigued, Damiot soon discovers that the last of the De Mohrts, a severely crippled genius, is indeed in residence--with a scientific lab in full swing..." -- Kirkus