Billie Carol is a 15-year-old girl who is not like every other teen. With her bobbed haircut, tomboyish behavior, and passion for track running, she distances herself from her fellow female classmates. Instead, she befriends Mike Benson, the newest school student who has recently joined the school athletic team. She gives him advice on how to run faster, and although he is initially reluctant to be taught a man's sport from a girl, he soon notices how gifted she is and is happy to listen to her. One day, the school coach Jones, sees her running on the track, and allows her to be on the team.

The town is shocked by this event, with most people feeling that it is inappropriate for a girl to be associated with athletics. Billie is unaffected by the gossips and criticism, though she feels sad over how much trouble she is causing her father, Howard. Howard is running for Mayor against Charlie Davis, and is harmed by the string of negative publicity. He at first sticks by his daughter's side, but later, as the elections near, attempts to make her quit the team. This upsets Billie, who has immediately been accepted as 'one of the guys' on the team. She reveals that she is able to run quickly due to listening to a fast beat in her head, and teaches the other guys how to do the same. During this process, she grows closer to Mike.

Meanwhile, Billie's older sister, Jean, has returned from college to spend time with her family. Jean admits to her sister that she has been married to a man, Bob Matthews, for seven months. Furthermore, she finds out that she is pregnant with his child. Howard is not aware of Jean's situation and encourages her to date other men, setting her up with Matt Bullitt. When the scandalous news about her pregnancy comes out, Howard's chances of becoming a mayor appear to dwindle. To save her father's career, Jean overcomes her fear and reveals that she has been married to Bob for over a year. Howard is at first shocked and slugs Bob, but later accepts and even embraces the news.

In the end, Billie wins the big match and becomes Mike's girlfriend. Afterward, he makes clear that he has no trouble with the fact that she is better at sports than he is. Howard wins the election, and becomes the town's mayor. His loving and caring wife, Agnes, reveals that she is pregnant at the post-election party.

• List of American films of 1965
• List of films about the sport of athletics

• Billie at IMDb  
• Billie at AllMovie
• Billie at the American Film Institute Catalog
• Billie at the TCM Movie Database