In early fourteenth-century China, Oyuna tells her granddaughter of her girlhood in Mongolia and how love for her horse enabled her to win an important race and bring good luck to her family.

Twelve-year-old Colton, son of a black mother and a white father, takes a job with the Pony Express in 1860 after his father abandons the family on their California-bound wagon train, and risks his life to deliver an important letter that may affect the growing conflict between the North and South.