The wild one

It's been two years since Sam's horse, Blackie, threw her in a near-fatal accident. She' been separated from her family, her ranch, and the wild mustangs she loves. Now she's home again, but her beloved horse has been missing since that fateful day. Then one night, a mustang comes to Sam. Is it Blackie, grown up and got wild? Is it the legendary stallion know as the Phantom? Or could it be both?