Monsieur Drain (a teacher): I may be reactionary, but this is absolutely astounding – the legal wife consoling the mistress! No, no, and no!
Christina Delassalle (Vera Clouzot) suffers greatly at the hands of her abusive husband Michel (Paul Meurisse), who is headmaster of a boys’ boarding school. She inherited this school from her family, but it’s clearly Michel who is in charge. Christina and Nicole Horner, one of the other teachers/Michel’s former mistress, decide to kill him! Christina (who has a serious heart condition) is terrified when- by chance- she meets a retired police inspector curious about the case.
Michel: [embarrassing Christina in the dining room while she is trying to eat some distasteful fish] Everyone is looking at you. Swallow.
Nicole: It’s disgusting!
Nicole: [angrily] Some things are hard to swallow, and I’m not talking about the fish.
When director Henri-Georges Clouzot bought the rights to the novel, he beat Alfred Hitchcock by only a matter of hours. Hitchcock was a big fan of this movie; some critics think that it influenced Psycho (1960). The message during the end credits was one of the first examples of a spoiler alert, requesting the audience not to disclose the plot. One of the posters said: “See it… be amazed by it.. but… be quiet about it!” Like most murder mysteries, the story is improbable; the film is entertaining, in part to plot twists and turns. The B&W lighting creates a noirish/sinister atmosphere. In the final 10 mins. we find an ending that is bound to scare (even modern/savvy audiences)!
Christina: Don’t you believe in Hell?
Nicole: Not since I was seven.
Christina: I do.
Filming took much longer than expected; the shoot was originally scheduled for 8 weeks, but ran for 16 weeks. This caused tension between Henri-Georges Clouzot and Signoret; Vera (also the director’s wife) tried to be a mediator. The co-leads couldn’t be more different from each other, though they are involved w/ the same man. Christina is delicate, petite, and wears conservative A-line dresses. She has two long braids that connect down her back (adding to her girlish qualities). Nicole is robust, tall, and wears blouses and pencil skirts. She has very short/blonde hair (reflecting her more modern personality). Christina is very religious; she has a small Catholic shrine in one area of her bedroom. While Christina (who can barely hide her nervousness) feels guilty, Nicole (cool as a cucumber) acts like planning a murder is no big deal.
Some viewers balk at reading subtitles- we should feel sorry for them! Others avoid unusually intense movies where the tone created makes the viewer feel uneasy. The crumbling boarding school where the main characters live doesn’t look pleasant at all. The swimming pool is filled w/ murky water, which makes it appear ominous. The teachers have to sit at the nasty headmaster’s table and eat old fish; only one glass of wine is allowed. Nicole’s apt. back in her small hometown seems stuffy and claustrophobic.
 From the very start it is very clear that all is not as it seems. But why? And who? What is the terrible secret of the swimming pool and later on, the bathtub? As the tension builds to an unbearable climax, we sit and hide behind our hands, peering through the gaps in our fingers. Oh my God!! It can’t be! It is!
 This movie does not offer cheap, pop out and scare you tactics. Rather, it makes the viewer expect things to happen that don’t. You wait on the edge of your seat for the quick jump out and scare you event to take place, but instead, it sneaks up from behind you. What an effect!
Les Diaboliques is a classic film that delivers the complete suspense package. It’s not surprising that many suspense movies of the modern era have tried to copy the plot.
 I remember when I first saw this. Nothing scary at first, but the nastiness of the place and the people is effortlessly shown. And then the bad stuff starts to happen.
-Excerpts from IMDB reviews