The butler of the Monferville estate finds a 17-year-old in a pitiful condition. The teenager claims to be Herminien, a son of the family who disappeared 6 years ago. Camille is looking for her son Léo.
A woman is found dead in the steam room of a spa. She looks 20 years younger than she is. Investigations take Niémans and Delaunay to the next village. Delaunay meets a white witch in the woods; Niémans discovers that the murder is reminiscent of medieval witch hunts.