Fourteen year old Clay Lancaster has never been more excited in his life. He and his big brother Mike are setting off on a road trip. They are headed from Seattle to Utah to find their uncle who they haven't heard from in several years. Two weeks into the trip, Mike wants to give up and go home. Clay convinces him to leave him behind so he can work at a little trading post and keep searching for their uncle. After Clay had only been there a few days, he was offered a job at a different trading post even farther out into the middle of nowhere. He accepts and learns a lot from the owner, Weston. One day, an old Navajo couple comes in and recognize the picture of his uncle. In their broken English, they manage to tell him where his uncle is.
Clay decides to go and find him. With a few supplies as possible and his trusty burro, Pal, Clay sets out across the open desert to the place the old couple told him. It's a long, arduous journey, but he eventually makes it. He is warmly welcomed by the Navajo people who live there, and he makes many friends. They tell him that his uncle was supposed to have returned several days ago with a herd of horses, but they have yet to hear from him.
Clay doesn't want to sit around and wait, so he sets out again, this time for the small town of Escalante. Upon arriving, he is surprised to find his uncle in jail for stealing horses. He believes what his uncle did was right, because otherwise the horses would have been slaughtered and made into dog food. The horses are the last wild mustangs in that area of the country and he feels that they must be protected.
One night, during a community dance and hoedown, Clay springs his uncle from jail, with the assistance of another local girl. They round up the horses and drive them back into Arizona where they and his uncle will be safe forever.