In a sleepy Provencal village, retired postman Emile Pencenat is busy digging his own grave when he spots an unstamped letter in the cemetery's disused postbox, addressed to a Madamoiselle Champourcieux. He dutifully posts the letter. When the body of this same Madamoiselle is later discovered - pinned to her piano with an ancient bayonet - Commissaire Laviolette is coaxed out of retirement to solve one of the most bizarre crimes imaginable.