Samantha discovers a plot to wipe out the wild horses near her family's ranch, but she can't convince anyone else that the Phantom's herd needs help.  
When her insistence that the mustangs are in danger pits her against her family, her classmates, and the local sheriff, her only friend left is the Phantom Stallion. Can he help her solve the mustang mystery before her dad sends her out of harm’s way, back to San Francisco?