Widower Doug Simpson (Danza) is a radio producer from California who lives with his two daughters, Katie (Dolenz) and Bonnie (Laura Mooney). When his oldest daughter (Katie) turns 15, she suggests to her father that's it's time for her to start looking more grown-up. For the last 14 years, Katie had been wearing dowdy clothes, braces, and thick glasses and hanging around with Richard, her next-door neighbor and long-time boyfriend (who had won Doug's approval); but when Doug leaves on a business trip, Katie transforms herself, along with the help of Doug's fiancée Janet Pearson (Hicks), into a knockout beauty.

When Doug returns, he is shocked to find boys from every walk of life interested in dating Katie. Janet suggests that Doug needs psychiatric help when his obsession with Katie and her boyfriends reaches extreme limits, and Doug seeks out an expert who gives him advice that goes wrong whenever Doug applies it. Throughout the latter half of the film, Katie maintains three boyfriends, two of whom she eventually stops dating. At the end of the film, Katie takes a class trip to Europe and reunites with Richard again – at which point Bonnie, her younger tomboy sister, begins her own dating spree. Doug also find out that the "expert" never actually had any practical advice, as he had never had a daughter himself.