A handsome, charming man named Fred begins renting a room in the attic of a quiet house owned by a lonely, plain-looking woman named Martha (or similar). Martha is shy, socially isolated, and desperate for affection.

Fred seduces Martha, and she falls deeply in love. He promises her marriage and a future. However, Martha discovers Fred is already married and has a criminal record. When she confronts him, he doesn’t leave — instead, he manipulates her into believing his wife is evil and that they can be together if "something happens" to the wife.

Martha helps Fred imprison his wife in the very same attic (or another hidden room), intending to starve her or kill her. But the wife escapes or is found. The plan unravels. In the 2018 version, the tension escalates into a violent confrontation where Martha realizes Fred never loved her — he was using her as an alibi and a tool.