Joyce Reynolds and Janis Paige play feuding and friendly stepsister romantic rivals in this riotous romantic comedy adapted from a hit Broadway play. All is status quo at the Linnett household: The boys come calling on Joy (Paige), Jackie (Reynolds) tends to her studies, and each parent (Barbara Brown and Edward Arnold) frets about their biological child. The sand in the oil arrives in the form of an old acquaintance, Warren James (Robert Hutton), who has matured somewhat since the stepsisters last saw him. Jackie is overjoyed when Warren first falls for her and asks her to the country-club dance, but all her romantic dreams fly out the window once Warren gets gobsmocked by the sight of Joy in a swimsuit. Sick of being beaten out, Jackie decides to join Joy -- and how -- on the flirty side of things, and undergoes a makeover with surprising results. - Plain Jane rivals sister for guy at country-club dance.