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Inventor Walter Randall (Jerome Thor) is saddled with a nasty wife named Laura (June Vincent), who is insanely jealous of her husband's romance with Phyllis Hudson (Marianne Stewart). Setting a time bomb to destroy Walter's newest invention, an underwater sounding device, Phyllis decides to literally kill two birds with one stone by knocking out Phyllis and leaving her to die in the explosion. Fortunately, Phyllis escapes in the nick of time; unfortunately, she is subsequently charged with Laura's murder. Attorney Perry Mason (Raymond Burr) relies upon an elaborate (and expensive) courtroom demonstration to save Phyllis from the gas chamber.