Margaret (Shirley Temple) and her uncle, Shawn (Barry Fitzgerald), move from Ireland to the United States to distance themselves from the death of Margaret's brother, a jockey. Shawn, a horse trainer, finds Seabiscuit, a horse he insists will be a champion racer. Margaret falls for jockey Ted Knowles (Lon McCallister), whose job reminds Margaret of her deceased sibling. Ted wants to get married, but she refuses unless he gives up his career -- and the chance to ride Seabiscuit to glory.