The wife of a cruel headmaster and his mistress conspire to kill him, but after the murder is committed, his body disappears, and strange events begin to plague the two women. The 1955 thriller/horror/noir film, Diabolique, is an intense ride reminiscent of Hitchcock at his Psycho best. Simone Signoret and Paul Meurisse star in this "Extraordinary new motion picture" with an ending best kept a secret for optimum enjoyment. Believe me, the sign says so.
If this movie sounds familiar, you may be remembering the Sharon Stone version from 1996. The 90s setting and attitude isn't quite as intense, gritty or subversive as the 50s version - but if you're too lazy to read subtitles, it's always an alternative.