Labbé, a hatter in a French provincial town, appears to lead the life of a respectable citizen but is in fact a serial murderer.

After getting drunk, he visits his favourite prostitute, Berthe, and kills her; he is found at the scene of the crime in the morning by police.

Again he pays homage to Hitchcock with a psychopath, Michel Serrault, who murders his wife, then kills six of her elderly friends.

[2]From Time Out London: The hatter (Serrault) is a mass strangler who allows his secret to be discovered by hangdog Cachoudas (Aznavour), the tubercular Armenian tailor opposite.

The ensuing relationship seems unbelievably reckless, even with a mad hatter involved, and manifestly it's the Hitchcocko-Jesuitical theology about shared guilt which animates the picture... Chabrol locates his adaptation in an off-kilter time zone – little bit '30s, little bit '50s – that some may find the most intriguing aspect of the movie.