Gaslight is a psychological thriller film directed by George Cukor and released in 1944. The film is based on the play of the same name by Patrick Hamilton and stars Ingrid Bergman, Charles Boyer, Joseph Cotten, and Angela Lansbury.
The film is set in London in the late 19th century and follows the story of Paula Alquist (Ingrid Bergman), a young woman who inherits a house from her aunt, a famous opera singer who was murdered in the house ten years earlier. Paula moves into the house with her new husband, Gregory Anton (Charles Boyer), a man she met and married in Italy. Soon after they move in, Paula begins to hear strange noises and sees the gaslights in the house dimming and brightening for no apparent reason. Gregory dismisses her concerns and convinces her that she is going mad, which leads to a series of events that make Paula doubt her sanity.
The film opens with Paula as a young girl watching her aunt, Alice Alquist, a famous opera singer, being strangled by an unknown man. The murderer is unable to find a valuable piece of jewelry that Alice had hidden, and he flees the scene. Ten years later, Paula is living in Italy and studying to be an opera singer under the guidance of her aunt's former accompanist, Maestro Guardi (Sir Cedric Hardwicke). It is here that Paula meets Gregory Anton, a charming and sophisticated man who shows a keen interest in her. They fall in love and get married, and Gregory suggests that they move to London and live in the house Paula inherited from her aunt.
As soon as they move in, strange things begin to happen. The gaslights in the house flicker and dim, and Paula hears footsteps in the attic. Gregory dismisses her concerns and tells her that she is imagining things. He convinces her that she is forgetful and absent-minded and that her aunt suffered from the same mental illness. He tells her that he loves her and wants to help her, but she must trust him completely.
Gregory's gaslighting of Paula intensifies as the film progresses. He convinces her that she is losing her grip on reality and that she needs to see a doctor. He takes her to see Dr. Brian Cameron (Joseph Cotten), a psychiatrist, whom he has chosen because he knows that Cameron was in love with Paula when they were younger. Cameron recognizes Paula's distress but is initially taken in by Gregory's charm and smooth-talking. However, as Paula's condition worsens, Cameron becomes suspicious of Gregory's motives and begins to investigate.
Meanwhile, the police have reopened the case of Alice Alquist's murder, and Inspector Brian MacDonald (Tom Stevenson) begins to question Paula about the night of the murder. Gregory becomes increasingly agitated and tries to prevent Paula from talking to the police. He tells her that they will think she is crazy and that she will end up in an asylum. He also suggests that she is becoming dangerous and might harm him or herself.
Paula becomes more and more isolated, and her mental state deteriorates. She becomes dependent on Gregory for everything, and he takes advantage of her vulnerability. He tells her what to wear, what to say, and how to behave. He even arranges for her to have a nervous breakdown in front of Cameron, hoping to convince the doctor that she is beyond help.
The climax of the film takes place on the night of a big party that Gregory has organized. He plans to search the house for the valuable jewelry that Alice Alquist hid before her death. He sends Paula to her room and begins to ransack the house. Cameron arrives and confronts Gregory, and the truth about his motives is revealed. Gregory is the unknown