Henri-Georges Clouzot's Les Diaboliques (1955)

Les Diaboliques is a kind of thriller with a horror-type ending and is a regular feature in most best French film lists. It was inspired by the novel Celle qui n'était plus (1952) by Pierre Boileau et Thomas Narcejac, and part of it (the 'murder' especially) is set in Niort, where Clouzot was born.

Essentially, there are four important characters here: Nicole (Simone Signoret), who works as Latin teacher in a private boarding school run by the tyrannical Michel Delassalle (Paul Meurisse), who is Nicole's lover and is married to the English teacher Christina (Véra Clouzot, the director's wife). The other person is Commissaire Fichet (Charles Vanel), on whom the eponymous detective in the American series Columbo (Peter Falk) is widely thought to be based.

Both Nicole and Christina detest Michel, who is not only violent towards them but callous towards his students, providing them with substandard food: this is ironic, though, as the money which oils the school's machinery comes from the very rich Christina. So they (or rather Nicole with the Catholic Christina's hypocritical agreement) decide to kill Michel: he is lured to Niort where he is put to sleep with a drug in his whisky which Nicole provides, and then (with Christina watching on) Nicole drowns him fully clothed in the bath. All that remains with the two women is to cart the body back in the school laundry basket and dump him in the school swimming pool.

But there's a problem: Michel has of course disappeared from school but even after the pool is drained he is not there: consternation for his women, and even more so when the suit he was wearing is delivered fully laundered by an outside firm. And to complicate things even further, there are reports of sightings of him in the school, even (it seems) in a new school photograph. Clearly, this is a case for Commissaire Fichet, who intervenes and carries out his own investigations, much to the fear of Nicole and Christina.

Christina has a weak heart and any disturbance can upset her, and it's hardly surprising that when she hears strange noises in the school late at night that she is very much alarmed. But her death blow comes when she sees her husband in the bath, rising as if from the dead and removing his false 'eyes of death': many viewers were stunned by this, so Christina's fatal collapse is understandable. And just as the two lovers Michel and Nicole prepare to celebrate their new fortune (Michel inheriting his late wife's wealth), Fichet immerges from the shadows to reveal that the sentence will be between fifteen and twenty years' imprisonment, depending on the skill of the lawyer.