In the hills of Tennessee, Shane Carson, a gifted, nationally-recognized horseman, is living the good life. When a mysterious mustang shows up on his farm, Shane doesn't know how--or why--the horse appeared, but the horse's distinctive brand identifies her. She is one of the Spirit Horses, a rare, wild herd that runs free on the Shoshone reservation in Wyoming. Watched over for centuries in the tribe's ancestral valleys, these exquisite horses, according to belief, provide a link to the afterlife. When tragedy strikes in his life, Shane nearly loses his will to live--but for one promise.