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Philippe Leroy stars as power boat racer Marco Breda, who has been struck with amnesia following brain surgery for a boating accident. While Marco recuperates at his remote villa, he begins romancing a young woman named Terry (Rossana Yanni), leading his jealous wife, Monica (Elga Andersen), to instigate a fatal struggle. Terry and Marco dump Monica's body in the ocean while people start getting murdered left and right, mostly by strangulation (although Marco's friend, Tommy [Franco Ressel], is graphically disembowelled). A police inspector shows up, and Marco is shocked to see Monica too, alive and well. Monica had been plotting with Marco's friend, Burt (Ivan Rassimov), to drive him insane, and the plot works, as Marco drives his car off a cliff shortly thereafter. What Monica doesn't know is that her double-cross wasn't so well advised, being that she is being triple-crossed by Burt and his mistress, Terry, who were also plotting to kill Marco and were using her to do it. Understandably upset by this turn of events, Monica kills them both, but that's when the real terror begins, as a mysterious stranger stalks her while she is alone in the house. Franco Fantasia and Carla Mancini co-star.