The experiences of a mouse-colored horse from his birth in the wild, through his capture by humans and his work in the rodeo and on the range, to his eventual old age.

While visiting their Uncle Bill on his ranch, two city kids learn the ways of the western range.

Having gotten his first horse, Big-Enough, for his fourth birthday, Billy spends the next several years working hard to become a good, all-around cowboy on his father's ranch.