When Pipe Bearer, the youngshamanof the Elk-Dog people dreams of a powerful spirit-horse--one bearing distinctive, hat-like markings on its head and ears--he knows he is being sent an important message. But he cannot interpret its meaning. Soon after, a colt is born bearing the exact markings he dreamed about and he is directed to undertake a long quest to the lands of the Pawnee and Lakota in order to learn the meaning of this event. Disguised as traders, he and his wife, Otter Woman, will encounter many wonders and not a few dangers before they discover the meaning of the colt with the Medicine Hat.