 In London, at Thorton Square 9, the prima donna Alice Alquist is strangled and her famous jewels miss. Her young niece Paula (Ingrid Bergman) is sent to Italy to study music and the house stays empty. Ten years later, Paula decides to get married with the older pianist Gregory Anton (Charles Boyer), who convinces her to move back to the old address in London. When they arrive, Paula finds a letter from a mysterious and unknown Sergis Bauer, making Gregory upset. He psychologically begins to torture Paula and she has a nervous breakdown, insecurity and memory problems. When the Scotland Yard policeman Brian Cameron (Joseph Cotten) sees Gregory Anton [the couple] in a tourist place, he immediately recognizes Gregory [he see Paula who reminds him of her aunt; he does not know Gregory] and decides to investigate and find evidences to connect Gregory with the unsolved murder, while Paula is being driven mad and menaced of being interned in an asylum by her husband.