The film opens with a haunting female voiceover: > "Last night I dreamt I went to Manderley again," accompanied by visuals of a desolate country manor. The story centers around a very young and nameless woman, portrayed by Joan Fontaine, who serves as a paid companion to the wealthy yet insufferable Edythe Van Hopper, played by Florence Bates. While in Monte Carlo, the protagonist encounters the distinguished widower, Maximilian (Maxim) de Winter, brought to life by Laurence Olivier. Their romantic connection blooms swiftly, and within a mere fortnight, they are wed.
Maxim ushers his new bride to Manderley, a grand country estate located in Cornwall, England. Here, they are met by the cold and oppressive housekeeper, Mrs. Danvers, portrayed by Judith Anderson. Mrs. Danvers harbors a deep obsession with the late first Mrs. de Winter, Rebecca, revered for her striking beauty, intelligence, and sophistication, and keeps her former bedroom maintained as a sort of shrine. Complications arise when Rebecca's unsavory cousin, Jack Favell, played by George Sanders, unexpectedly visits while Maxim is away.
As the new Mrs. de Winter grapples with her newfound responsibilities, she becomes increasingly insecure about her marriage. The specter of Rebecca looms large, leading her to believe that Maxim's heart still belongs to his deceased wife. Moments of tension surface as she unintentionally provokes Maxim's anger over seemingly benign actions.
In an attempt to become the ideal wife, she persuades Maxim to host a costume party, reminiscent of the celebrations he held with Rebecca. While preparing her costume, Mrs. Danvers maliciously suggests she model herself after the exquisite outfit of Caroline de Winter, an ancestor. The evening of the party unveils the protagonist's attire, which horrifies Maxim as it mirrors the dress Rebecca wore at their last ball before her demise. In a climactic confrontation with Mrs. Danvers, she is chillingly informed that she can never replicate Rebecca, with Danvers nearly coercing her into a leap from a height.
Amidst this turmoil, word spreads of a shipwreck, leading her outside where it's revealed that a sunken vessel holds Rebecca's body. In a moment of intense revelation, Maxim confesses that he had previously misidentified another body as Rebecca's to cloak the shocking truth. Their marriage began under a pact: Rebecca would masquerade as the ideal wife while pursuing her promiscuous lifestyle. When Rebecca later discloses her pregnancy with Jack Favell's child, a heated altercation ensues in which she tragically falls and dies. In a desperate act, Maxim disposes of her body in a boat, which he scuttles.
As the layers of innocence peel away, Maxim's bride guides him on how to conceal the circumstances surrounding Rebecca's death from the authorities. During the ensuing police inquiry, deliberate damage to the boat suggests suicide, while Jack Favell attempts to leverage Rebecca's note, implying she was not suicidal. Favell's blackmail efforts provoke Maxim to confess to the police. Suspicions gather around Maxim as murder becomes a potential charge. Investigating further leads to questions about Rebecca's visits to a London doctor, with Favell assuming it was related to her pregnancy. However, the doctor’s conclusion reveals that Rebecca's concerns of pregnancy were unfounded; she had been battling late-stage cancer.
Ultimately, the coroner's findings lean toward a verdict of suicide, leaving Maxim, Frank Crawley (his steadfast friend and the estate's manager), and his wife as the only ones privy to the full narrative—a tragic manipulation where Rebecca incited Maxim to take her life as an indirect act of suicide.
The climax unfolds when Maxim returns to Manderley only to discover flames engulfing the manor, set by the deranged Mrs. Danvers. In a harrowing escape, the second Mrs. de Winter and the estate staff narrowly avoid the inferno, while Mrs. Danvers meets a tragic end amidst the flames.
