A man shows up at a woman's villa claiming to be her presumably deceased brother.

South African diamond company heiress Kimberley Prescott has returned to her family's villa in Spain to recover from the shock of her father's recent suicide and her brother Ward's fatal car accident. Late one night after Kimberley's maid Maria leaves, a well-mannered stranger walks into the villa claiming to be Ward and details events of their shared childhood. Horrified, Kimberley calls for the police, but when police investigator Vargas arrives and sees that Ward's papers and passport are in order, he accuses Kimberley of playing a game. Kimberley insists that the stranger looks nothing like her brother, whose body she identified at the time of the accident. She shows Vargas pictures of her brother, but the photos are of the stranger in the room. Ward explains that on the night of the accident he gave a ride to a man, who then stole his wallet and threw him from the car. The thief died in the accident, while Ward suffered from amnesia for months in a hospital. Desperate to prove the stranger wrong, Kimberley tries to call her uncle, Chandler Bridson, but receives no answer. After Vargas departs, Kimberley offers the stranger a huge diamond pendant to leave her alone, but Ward instead plays a family favorite on the piano and talks about their father. Hysterical, Kimberley runs to her car but finds the key is gone. Ward then hands her the key and taunts her about her hospitalization in a mental institution after the family deaths. Kimberley flees to her bedroom and, unable to reach her uncle, cries herself to sleep. In the morning, Ward announces that he has replaced Maria with a new "friend" named Elaine Whitman, hired a butler named Carlos and canceled her appointment with Chandler. Kimberley runs to the villa's beach house where she tries to call Chandler, but Ward interrupts. Kimberley, desperate to expose the imposter, calmly asks Ward to prepare her "swimming drink," but Ward adeptly completes the task and even remembers their family toast. After discovering that Chandler is out fishing, Kimberley drives to Vargas' office where the policeman assures her that even Ward's letter of credit at the bank is in order. Kimberley insists she identified her brother's body, but Vargas insinuates that she is suffering from "imagined crimes." Once outside, Kimberley finds her car is gone and Ward picks her up instead, suggesting she stop driving for a while. During the drive home, Ward shows her the cigarette case he received for winning a car race and recalls the thrill of the competition. Kimberley challenges him to beat his own time racing the curvy sea cliff road, hoping he will not remember his time or the route. After a harrowing ride in which Ward comes close to besting his previous race time, Ward asks Kimberley for the location of ten million dollars worth of diamonds that their father stole from the company before his death, but Kimberley claims the diamonds disappeared. They return home to find Chandler, who greets Ward warmly, as Vargas witnesses the reunion. Kimberley is heartbroken that Chandler appears to be in league with the stranger. Later, when Ward demands that she recount her travels after her father's death, Kimberley claims to have left the diamonds in Tangiers, where only her signature can release them. Ward then forces her to sign paperwork releasing the jewels to him. Later, Kimberley questions Ward's conscience and, although he reacts coldly, Ward is softened by her appeal. At midnight that night, Kimberley, hearing a car leave, searches the house in hopes that the her tormentors have gone. Finding the house empty, she returns to her bedroom laughing with glee until Whitman barges in and hands her tray with milk and a copy of Kimberley's will. Putting the will in her pocket, Kimberley runs to the beach house and, believing Ward has followed her, hides in the dark with a spear gun. She then shoots and misses the entering stranger, who is Vargas. When the policeman asks for the truth about the diamonds, Kimberley claims Ward stole the last remaining family asset from the vaults. Realizing her father would be destroyed by the betrayal, she begged Ward to reconsider, but her brother was a selfish man who only wanted money from the family. She learned soon after that he had died and found the diamonds in his personal effects from the accident. Kimberley planned to give back the diamonds to her father, but when she returned home, the police informed her that he had committed suicide. After her release from the mental hospital, Kimberley left the stones in Tangiers, rather than returning them to the company and uncovering the truth, which would have risked ruining her father's reputation. Vargas believes her and offers to help if she will return the stones to the company. Kimberley agrees and the two then plan to get the imposter's fingerprints to unravel the mystery. Later, when Kimberley flirtatiously offers Ward a glass of brandy, she surreptitiously switches glasses, leaving the snifter with Ward's prints on the bar counter for Vargas, while Ward takes her glass. Seeing Kimberley's lipstick on the glass, Ward and Whitman surmise that she has given the glass with Ward's fingerprints to Vargas. Later that night, Kimberley retrieves a lockbox hidden in the beach house chimney, but as she tries to sneak back into the house undetected, Chandler surprises her, causing her to faint. When Kimberley wakes up, she finds Whitman, Ward and Chandler standing over her and the diamonds and a new will before her. After forcing her to sign the will, Ward and Whitman then suggest Kimberley take a swim, and grabbing her by both arms, escort her toward the water, where she knows she will meet her death. Suddenly, Vargas arrives and informs Kimberley that the fingerprints match her brother's. Frantic, Kimberley begs Vargas not to leave her, insisting that Ward will drown her. Delirious, Kimberley sobs that she knows Ward is dead because she killed him. Having heard Kimberley's confession, the imposter reveals his real identity as Police Inspector Williams and calls Barcelona police headquarters to announce the resolution of the case. After Kimberley tells Chandler that she begged Ward not to take the diamonds and then laments that she did not stay by her father's side, the police agents arrest her.