Plot
After spending time in New York City, Julie Wardh and her diplomat husband Neil return to Vienna, where several women have recently been murdered by a suspect wielding a straight razor. Julie is delivered a flower bouquet with a sinister note from Jean, her former lover, with whom she had a sadomasochistic relationship that became abusive. At a high-society party, Julie's friend Carol introduces her Australian cousin George. Carol's and George's wealthy uncle has just died, and they are his only heirs. George flirts with Julie, who is unhappy in her marriage to the neglectful Neil. Julie leaves the party after noticing Jean, but Jean confronts her outside, alluding to their past and offering to drive her home. Neil intervenes and slaps Jean, who laughs and leaves.
After a lunch date arranged by Carol, Julie and George begin a romantic affair, despite Julie's initial reluctance. Julie receives an anonymous call from a blackmailer demanding 20,000 schillings not to tell Neil about the affair. Julie suspects Jean is the blackmailer, and Carol insists on meeting the blackmailer for Julie in Schönbrunn Palace Park, where she is murdered by an assailant wielding a straight razor.
Julie learns about Carol's murder and urges the police to investigate Jean, but Jean has an alibi. Julie is later attacked in the parking garage of her apartment building by a figure with a straight razor, but she escapes. After she tells Neil about the encounter, he arms himself with a handgun and orders her to take him to Jean's residence. There, the pair discover Jean in a bloody bathtub.
Terrified of staying in Vienna, Julie secretly leaves Neil to travel to Spain with George. Back in Vienna, one of the razor killer's intended victims kills him in self-defense. Julie is relieved after learning that the dead killer was a stranger to her, but someone continues to stalk her in Spain and sends her a note signed "Jean", causing her to have a nervous breakdown. When George goes to get a doctor, Julie is ambushed and knocked out with chloroform by Jean, who faked his death. He stages the kitchen to look like Julie has committed suicide by carbon monoxide poisoning. George and the doctor arrive to find Julie locked in the kitchen, from which they quickly remove her, and the doctor tries to resuscitate her as George calls for an ambulance.
At the police station, the police inform George and Neil, who has been summoned from Vienna, that Julie has died and that her death has been ruled a suicide. Neil angrily accuses George of murder, despite his being with the doctor. George secretly meets Jean, whom he hired to kill Julie. Jean demands his promised payment and fake passport so that he can flee to Rio de Janeiro, but George shoots him dead and stages his death as a suicide.
George meets with Neil, and their car ride conversation reveals that they conspired to murder Carol and Julie. Carol's death makes George the sole inheritor of his uncle's fortune, and Julie's death yields a huge insurance payment for Neil to avoid bankruptcy. To give each other alibis and shift suspicion onto the razor killer, Neil killed Carol in the park, and George tried to kill Julie in the parking garage, then hired Jean to kill her after the death of the razor killer and Jean's faked death.
Neil sees Julie standing on the side of the road, and he and George are suddenly pursued by police vehicles. While trying to evade the police, George and Neil drive off a cliff to their deaths. It is revealed that the doctor resuscitated Julie, but the police faked her death to trick George and Neil into meeting, having grown suspicious when Carol's death did not fit the razor killer's modus operandi . Julie is consoled by the doctor as they drive away.
