Radio producer and widower Doug Simpson looks after his two daughters, twelve-year-old Bonnie, and Katie, who is celebrating her fifteenth birthday. Encouraging Katie to broaden her horizons, Doug presents the girl with an airplane ticket for a school trip to Paris, France, but she is socially awkward, and wishes to stay home. Although Katie wears thick-rimmed eyeglasses and braces, she is adored by her nextdoor neighbor, Richard. On the night of her birthday, Katie confesses to her father that she intends to end the romance with Richard. Several days later, Doug returns home from a business trip to find that his girl friend, Janet Pearson, has given Katie a makeover, and the girl has been transformed into a knockout. Doug becomes obsessed with fending off the girl’s new suitors; he neglects his duties at work, and ratings drop at the radio show. Janet convinces Doug to seek treatment from Dr. Herman Fishbinder, but the psychiatrist argues that Doug is not overreacting. He gives Doug a book he wrote about controlling teen behavior, and suggests that Katie should take birth control pills. Although Katie still is a virgin, Doug fails to convince her of the merits of abstinence. Dr. Fishbinder advises Doug to get married, so his daughters will have a strong female role model, and he proposes to Janet. Overjoyed, Janet wants to make love, but Doug complains that women are singularly fixated on sex, and turns her away. In time, Doug befriends Katie’s musician boyfriend, Joey. Still, Katie ends the relationship and tells her father that she is enjoying her newfound popularity. Richard, the boy next door, tries to win back Katie’s heart, but she starts to date a wealthy senior named Timothy. Remembering Dr. Fishbinder’s book, Doug suspects the young man is “too perfect” and spies on his affairs. The obsession causes his radio show to suffer further, and ratings continue to decline. Doug forbids Katie from going to the prom with Timothy, but Janet appeals to her fiancé, and he capitulates. However, he learns from Dr. Fishbinder that most girls lose their virginity on prom night, and makes a dinner reservation at the same hotel so he can spy on his daughter. Seeing Katie and Timothy leave the dance early, Doug follows the couple to a motel party and pretends he is a room service waiter. Katie tells Timothy that she does not wish to have sex and asks him to take her home, but he is concerned about upholding his promiscuous reputation, and refuses to leave. Hearing commotion inside the bedroom, Doug kicks down the door and falls on top of Timothy as Katie runs away. Doug gives chase in a car and hears Dr. Fishbinder on his radio show, admitting that he does not have a daughter of his own. Enraged by the doctor’s deception, Doug drives to the station and yanks Fishbinder from the microphone. However, he trips and falls through the window, landing three stories below. Unharmed, Doug gives an account to police and Janet arrives with news that Katie has changed her mind about going to Paris, and is awaiting her plane. Police escort Doug to the airport, and he finds Katie just in time. He apologizes, and she admits he was right to mistrust Timothy. As Katie boards the plane, she reunites with the brokenhearted Richard, who is also attending the school trip. Back home, Doug learns that his on-air fight with Dr. Fishbinder caused an upsurge in the radio show’s ratings. He decides to co-host a program with the psychiatrist about child rearing.