This 1955 French film stars Simone Signoret, Vera Clouzot, and Paul Meurisse. It is set in a boarding school which is being run into the ground by Headmaster Michel Delassalle (Meurisse). Delasalle is married (his wife, Christina, is played by Clouzot) and has a mistress (Nicole Horner, played by Signoret) who also teaches at the school. The two other teachers at the school, the doorkeeper, the students, and sundry others can't stand the cad. Delassalle refuses to spend money on maintenance, decent food, and - horror of horrors for the French - good wine.
Delassalle is a despicable lout, and his wife and mistress decide to murder him. Signoret takes the lead and comes up with a credible plan giving them an alibi, and it goes off with those little hitches that keep you on the edge of your seat as you wait for various interlopers to discover the secret in the large wicker basket.
Once they've successfully carried out their plan, things go horribly wrong. The body disappears. The two murderers can't figure out where it went. Then Delassalle's suit is delivered by the dry cleaners. The two women get hints and clues, but they can't figure out who is out to blackmail them. The tension is really well done, subtly played by the actors and realistic. Signoret would have been perfect in a Hitchcock movie as the cold blooded "ice blonde" that Hitch preferred. As the tension builds, the two conspirators begin to fall to pieces and their relationship frays, then breaks. Everything that can go wrong does: a body is discovered in the Seine, but it's not Delasalle's. When Christina goes to the morgue, a detective sees her and offers to solve the missing husband case for her - and he won't take no for an answer.
The three actors were excellent. Meurisse captures the cruel coldness of Delasalle with fleeting expressions across his face that told more than dialogue. Clouzot was small and weak, well-cast as the invalid wife of the headmaster. But Signoret took center stage. While Christina was mousy and dark-haired, Nicole was man-sized and blonde, had plans, and executed them. As the tension mounts and they begin bickering, their relationship takes on overtones of a married couple.
The pacing of the film is decidedly Fifties, but bear with it. It soon picks up, and the relationship and tension between to two women is very well done
The plot was based on a novel, and it was later made into 1996's "Diabolique," with Sharon Stone, Isabelle Adjani, and Chazz Palminteri. I haven't seen that version. Instead, I'd recommend "Mademoiselle" with Jeanne Moreau if you like "Les diaboliques." Another teacher at a school in a small town runs amuck.