It’s the year 1912, and thirteen-year-old Erin Burgess has heard rumors about an old hermit who lives in the desert canyons near her home in southwest Texas. She thinks they’re just stories that adults tell to scare children, but when her family’s Missouri Fox Trotter mares escape with a herd of wild mustangs, she discovers that the myth is in fact a reality.

In an attempt to recapture their horses, Erin and her twin brother, along with the son of the ranch hands who take care of their property, are injured, and it is Old Wild Man Terry who saves them. Soon Erin learns that the kind but strange-looking man has a fascinating history that includes being raised as a Black Seminole Indian and protecting settlers along the border between the U.S. and Mexico from raiding Indians and outlaws. And, it turns out, he’s got a way with horses.