On the night of his 42nd birthday, George Webber, a popular songwriter, begins showing symptoms of "middle-age crisis." Over the succeeding weeks, he finds himself continually staring at young girls on the street, and he begins envying his high-living neighbor, whose life is one endless orgy. George's behavior causes great concern to his lover, singing star Samantha Taylor, and to his partner Hugh, who has seemingly avoided George's dilemma by being gay. While driving home one afternoon, George spots Jenny (Bo Derek), a stunning young beauty en route to her marriage ceremony. Regarding her as "the most beautiful girl I've ever seen" (on a scale from one to 10), George follows her to the church. He later learns her name, and discovers that she and her husband are honeymooning in Mexico. Driven by the impulse to see her again, George flies to Mexico and checks into the hotel where Jenny is staying. Later, he sees the couple on the beach, and begins indulging in romantic fantasies about the lovely young girl. When he rescues her husband from drowning, a grateful Jenny invites George to her room.