Polo pony raising and training in Colorado is the background for the story of Shadow, a boy, and a really fine horse, the Runner. Shadow, who is recovering from a recent attack of polio, limps and is often overcome by the weakening after effects of the disease. This and his differences with his Uncle Nathan, who thinks Shadow's dreaminess is only a sign that he is becoming a wastrel like his dead father, are complications in the more primary elements of the book- the Runner's training, the buying and selling of other ponies and the Runner's loss and final recovery. When the Runner is found Uncle Nathan and Shadow have also found each other.