Horse trainer Shawn O'Hara and his lovely niece, Margaret, come to America to escape the memory of an accident involving Margaret's brother, Danny. Working with thoroughbreds in Kentucky, Shawn takes a liking to a yearling named Seabiscuit, and fights to convince the horse's owner that the tiny horse with big knees will become a top-notch racehorse. Meanwhile, Margaret begins a tentative relationship with jockey Ted Knowles, but is haunted by her brother's death in a steeplechase spill.