Gaslight

In the late 19th century, aspiring opera singer Paula Alquist (Ingrid Bergman) and Gregory Anton (Charles Boyer), the accompanist at her singing lessons under the tutelage of Maestro Guardi (Emil Rameau) in Italy, fall in love and marry. Before learning of her background, Gregory is able to convince her to live in London, then when she divulges to him that she owns a house there at 9 Thornton Square, it bequeathed to her by her famous maternal aunt, opera singer Alice Alquist, who raised Paula and whom Paula found murdered in the house; the murder was never solved. Paula hadn't thought about the house in a long time, and believes that Anton's love can help her through the anguish of her aunt's murder enough that she can live there with him. Over time, Paula begins to forget things, lose things, and imagine things--such as an animosity with the new Cockney housekeeper Nancy (Angela Lansbury), who has a penchant for making "friends" with whatever Police Constable is patrolling the neighborhood--and Gregory quietly convinced her, without using the exact words, that she is ill. As such, she becomes isolated in the house, which only exacerbates her feeling that she indeed is going mad. However, two people on the outside believe that funny things are happening behind the closed doors of 9 Thornton Square, where only the domestics, Nancy and Elizabeth (Barbara Everest), are allowed in, and only Gregory, who ever leaves by himself to take a walk every night. Those two are: Miss Thwaites (May Whitty), an elderly busybody neighbor who loves a good mystery; and Brian Cameron (Joseph Cotten), a fan of Alice Alquist, and who, in his professional life, arguably knows the most about her murder besides the actual murderer.