Boys school headmaster Michel Delasalle (Meurisse) is notoriously cruel, an evil man without remorse and sans sympathy or understanding. He even openly taunts his adulterous relationship with his mistress Nicole (Signoret) in front of his wife Christina (Clouzet).

Christina and Nicole decide they've had enough of the tyrant's machinations. They put their heads together, and decide to bump off the malicious man and rid themselves of his evil once and for all.

Disposing of the body in the school's pool, the two women find themselves finally relieved of the heavy monkey once on their backs.

That is, until the pool is drained. And the body is nowhere in sight.

Who could have known about their secret plot? Did somebody see them commit the crime? What does the stranger want? Where is Michel's body?

Excellent every single moment, with stupendous performances from Clouzet and Signoret and a damp atmosphere of despair throughout.

A truly timeless ending and one of the best horror films ever.

Also known as The Fiends. French: Les Diaboliques.

Remade many times, but one notable standout is the above average TV thriller Reflections of Murder in 1974, starring Tuesday Weld and Joan Hackett.