Gaslight (1940)

There may be nothing more frightening than being a slave -- except, perhaps, not realizing you are being made into one. This British film (which was remade in Hollywood a few years later) is in some ways one of the most terrifying movies I have ever seen. In its opening frames we see an old woman strangled to death by an unseen assailant who then begins to tear apart the room looking for something. Later we meet Mr. and Mrs. Mallen. Apparently Mrs. Mallen has a tendancy to take things, but never seems to remember it after it has happened. Her husband subtly suggests that she's going crazy. Paul Mallen as played by Anton Walbrook is one of the most sinister characters in film. We soon realize that she is not going crazy, but he is effectively making her think that she is going crazy -- threatening to commit her, trapping her in the house, not allowing any visitors, but it's all for her own good and she has no reason to suspect that her husband may have ulterior motives. As far as psychological thrillers go, this is top-notch.