Nancy Drew, along with her friends Bess and George, go to Arizona to help relatives whose ranch is terrorized by a phantom horse and sabotage, threatening to ruin them. Nancy investigates a 19th-century outlaw's curse, hidden treasure, a kidnapped child, and a gang of thieves to save the ranch. The ranch is being haunted by a spectral horse linked to the legend of outlaw Dirk Valentine, who supposedly cursed the land. A series of deliberate accidents (rockslides, property damage) are intended to scare off the owners.