AllMovie

Paul Decker (Peter Van Eyck) arranges what seems to be the perfect murder of his wife, while at her home in Italy. Lightly drugging her into unconsciousness, he seals the room she is in and turns on the gas, and then dons a diving snorkel with hoses drawing air from the outside -- he remains hidden in the room beneath the floorboards even as the police investigate the crime scene. As far as they know, he was just over the border in France when Mrs. Decker committed what appears to be suicide -- and there is no reason to investigate further, beyond a routine inquest. But he doesn't bargain on Candy (Mandy Miller), his wife's daughter by her previous marriage -- she has long believed that Paul killed her own father, and is positive that he was responsible for her mother's death. Try as those around her -- including her guardian (Betts St. John) -- do to convince her otherwise, she won't let go of this idea. And when Paul kills Candy's dog Toto, she tells him he will have to kill her, because otherwise she will kill him. From that moment on, they are on a collision course, as Paul tries at once to protect himself, covering tracks that he never thought anyone would trace -- not having bargained on the obsessive girl -- and to discredit her in preparation for possibly having to kill her. Meanwhile, Candy waits, watches, and asks question after question, hoping for one clue or slip that will allow all of her suspicions to fall into place. And finally, after several rounds of cat-and-mouse, and a near-fatal encounter, they meet face-to-face at the scene of the crime.