In London, Lisa Baumer Lisa Baumer, who is entangled in an affair with George Barnett, learns that her husband Kurt Baumer has died in a plane explosion en route to Tokyo, and that she is set to receive a one-million-dollar life-insurance payout in Athens. Lisa's former lover Philip threatens to reveal a potentially incriminating letter unless she pays him off. A man with a facial scar murders Philip and steals the letter shortly before Lisa arrives at Philip's apartment.
Lisa travels to Athens, followed by Peter Lynch, an investigator for the insurance company. At a hotel restaurant, Lisa tells Peter that she is aware of his identity and that she did not kill her husband. Lisa goes to meet Kurt's mistress Lara Florakis and her hitman Sharif, who murdered Philip and stole the letter, unbeknownst to Lisa. Lara accuses Lisa of planning the death of Kurt, who allegedly intended to divorce Lisa, marry Lara, and make her his beneficiary. Lara threatens to blackmail Lisa or have Sharif kill her if she refuses to sign half the payout over to Lara. Lisa escapes, aided by Peter. The next day, Lisa cashes the insurance check and plans to catch an evening flight to Tokyo for a rendezvous with Barnett. Peter is nearly run over by Sharif while investigating Kurt's villa. Peter and the hotel staff discover that Lisa has been murdered and that the money has been stolen.
Police inspector Stavros and Interpol agent Stanley investigate the case. Stavros informs Peter that he is a suspect and confiscates his passport. Peter tails Stanley to Lara's apartment. Lara insists to Stanley that she did not kill Lisa. Sharif nearly kills Peter then flees. Peter accuses Lara of having Lisa killed and trying to kill him, which she denies.
Peter meets Cléo Dupont, a journalist assigned to the case, and the two start an affair and investigate together. Sharif ransacks Peter's hotel room but finds no evidence to implicate Peter in Lisa's murder. Lara and Sharif are murdered. Stanley tips Cléo off about the murders. After Peter leaves Cléo's apartment, a figure tries to murder Cléo. Peter returns to the apartment, having forgotten his car keys, and the figure flees. Stanley discovers a scorpion-shaped cufflink on the floor. Lisa's lover Barnett is murdered in an Athens hotel room belonging to his mistress; the pair are revealed to be flight attendants. Peter acquires a photograph of Kurt wearing a scorpion cufflink. Peter and Cléo work with Stavros and Stanley to theorize that Kurt faked his own death, possibly with Barnett's help, then murdered Lisa, Lara, Sharif, and Barnett to claim the insurance payout and frame Peter. They arrange for Peter to take a vacation with Cléo in the Saronic Gulf, pretending that he is a fugitive from justice in order to lull Kurt into a false sense of security.
During Peter's and Cléo's getaway, Cléo observes Peter scuba diving into a cave with a sack allegedly containing spare harpoons and other equipment, then emerging with the sack apparently empty. Later, while he sleeps on the boat, Cléo investigates the cave and discovers the sack with one million dollars inside it. Peter apprehends her and takes her back to the boat, where he reveals that he plotted the deaths of Kurt and Lisa with Barnet to claim the insurance payout while making it seem that Kurt faked his own death, stole the payout from Lisa, then killed her, Lara, Sharif, and Barnet to cover his tracks. He also had Barnet attack Cléo and leave behind the scorpion cufflink as part of the effort to make the authorities suspect Kurt. Peter asks Cléo to escape with him, but she rushes to the radio to call for help, stabs Peter's shoulder with a harpoon, and flees ashore with Peter in pursuit. Peter attacks Cléo, but police suddenly shoot him dead. They deduced Peter's scheme from Barnet's mistress's mermaid brooch of similar make to the scorpion cufflink, which was a counterfeit of Kurt's. After Cléo recovers in a hospital, Stavros sends her off in a taxi with Stanley, who suggests that he would like to take her on a date.
