A religious fanatic imprisons her late son's sinful fiancee.

Mrs. Trefoile, an aging religious fanatic who lives in a desolate country home in an English village, devotes her days to reading the Bible and mourning her son, Stephen, who died a few years earlier in a car crash. Her only companions are a sullen housekeeper, Anna; the woman's brutish husband, Harry; and an imbecile gardener, Joseph. One day she receives a courtesy visit from her dead son's former fiancée, Patricia Carroll. Upon learning that Patricia is soon to marry, Mrs. Trefoile locks the young girl in the attic and prepares to "cleanse her soul" so that she will be fit to be reunited with Stephen in the hereafter. All of Patricia's efforts to escape are thwarted until she tempts the lecherous Harry into releasing her, but the plan fails when the now totally deranged Mrs. Trefoile kills Harry in the basement of the house. Eventually, Patricia's fiancé, Alan Glentower, becomes so worried about her absence that he drives to the village. Mrs. Trefoile tells him Patricia has already left, but he discovers the truth and breaks down the cellar door just as the crazed woman is about to perform a death ritual over the terrified Patricia. While Alan telephones the police, Anna, having discovered her dead husband's body in the basement, stabs the old woman in the back. As she dies, Mrs. Trefoile embraces her dead son's portrait and murmurs, "Stephen, they hurt me."