The Spiral Staircase is a 1946 thriller directed by Robert Siodmak, starring Dorothy McGuire, Kent Smith, and George Brent.
McGuire is Helen, a maid in the splendid Warren family mansion in early 19th-century New England. The community has been disturbed of late by a Serial Killer who preys specifically on women who have some sort of disability—in the past the killer's victims included a woman with a badly scarred face and a "simple-minded" woman, and the film opens with the killer strangling a woman who has a lame leg. This news is being taken very seriously indeed in the Warren mansion, as Helen is a mute, having fallen into psychosomatic muteness as a child when she saw her parents burned to death in a fire. As soon as the latest murder is reported, everyone starts pleading with Helen to flee the town, especially good-hearted Dr. Perry (Smith), who is in love with Helen.
Besides Helen, the household consists of cantankerous old Mrs. Warren (Ethel Barrymore), who is bedridden, her ne'er-do-well son Steven Warren, and her stepson Professor Albert Warren (Brent), son of the late Mr. Warren's first wife. The Warren half-brothers don't like each other very much, with serious Albert being regularly irritated by rapscallion Steven, and both brothers being rivals for the hand of Blanche (Rhonda Fleming), the lovely secretary to the Warren family. Also present in the house are Mr. Oates (Rhys Williams), the handyman, and his wife Mrs. Oates (Elsa Lanchester), the cook.
- Chekhov's Gun: A literal gun, which Mrs. Warren has by her bedside and which a horrified Helen tries but fails to wrest away from her. At the climax Mrs. Warren saves Helen's life by shooting Albert dead with said gun.
- Chiaroscuro: Used for many, many shots in an old Edwardian manor that doesn't appear to have electricity hooked up and is still lit by gas lamps and candles.
- Creator Cameo: The close-ups of the killer's eyes and hands are close-ups of Robert Siodmak.
- Cute Mute: She sure is cute, but Helen's muteness unfortunately makes her the target of a serial killer. It also prevents her from getting help at the climax, like when she calls the telephone operator only to be unable to get any words out.
- Dumb Struck: Helen is not mute because of physical trauma, but from emotional trauma after seeing her parents burn to death.
- Empathic Environment: A driving rain and thunderstorm throughout set an appropriate mood for a tense Serial Killer thriller.
- Extremely Short Timespan: Takes place over a single afternoon and evening, as Helen is stalked by a demented killer.
- Foreshadowing: Mrs. Oates the alcoholic laughs when she tells Helen about how she dropped a candle and stole a bottle of brandy in the dark basement. Later, this is how Helen manages to lock Stephen in the vault.
- Imagine Spot: After Dr. Perry kisses her, Helen has a long Imagine Spot in which she visualizes their wedding, but it ends badly when she can't say "I do" even in her own fantasy.
- Lady Drunk: Mrs. Oates, who is quite upset when her husband takes away the brandy, and then later deliberately drops a candle in the basement so Albert won't see her steal another bottle of brandy. When Helen needs help at the climax, Mrs. Oates is passed out drunk in the kitchen and Helen can't rouse her.
- Love Triangle: In the backstory between Blanche, Albert, and Stephen. Blanche chose Stephen but isn't too thrilled about it.
- One-Eyed Shot: Used when the killer is stalking both of his victims as well as when he is staring at Helen.
- P.O.V. Cam: Used from the POV of the murderer as he's staring at his two victims as well as when he's stalking Helen. In fact, this is combined with One-Eyed Shot, as the POV shot is super-imposed over the extreme close-up of the killer's eye.
- Serial Killer: One that stalks women who have some sort of handicap or deformity. Blanche's murder doesn't fit with this description, however, suggesting a more personal motive. Maybe he's just so far over the deep end that "doesn't want to be with me" looks like weakness to him.
- Sexy Secretary: Blanche the curvy secretary, who occasionally writes letters but seems to exist more as an object of rivalry for the Warren brothers. At some point in the past she rejected Albert and embarked on an affair with Stephen, but the crudeness of Stephen's advances make her decide to leave the house.
- The Social Darwinist: The villain cites this as his reason for killing women with any sort of physical defect, such as the mute heroine:"There is no room in this whole world for imperfection. What a pity my father didn't live to see me become strong, to see me dispose of the weak and imperfect of the world, whom he detested. He would have admired me for what I am going to do."
- Wham Line: How Albert is revealed as the killer, after seemingly coming to the rescue of Helen."You tried to call for help, didn't you? I'm glad you didn't."