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Though not readily apparent by its title, The Four-Sided Triangle belongs in the realm of science fiction/fantasy. Barbara Payton stars as Lena, a British girl raised in America who returns to her hometown on a sentimental journey. Here she is reunited with her childhood friend Bill (Stephen Murray), now a scientist. With the help of his pal Robin (John Van Eyssen), Bill has developed a duplicating machine (today it'd be called a cloning device). When Robin and Lena fall in love, the heartbroken Bill decides to create a duplicate Lena, whom he names Helen. Unfortunately, since Helen is an exact copy of Lena, the clone falls in love with Robin as well. A climactic fire claims the life of one of the two Lenas--but which one? Director Terence Fisher co-adapted the screenplay from a novel by William F. Temple.