The mysterious Don Del Oro ("Lord of Gold"), an idol of the Yaqui Indians, plans to take over the gold and become Emperor. Francisco was put in charge of a legion to combat the Yaqui tribe and protect the land, but when attacked Zorro came to his rescue. Francisco's partner recognized Zorro as the hidalgo Don Diego Vega, then ask him to take over the fighting legion as his alter-ego Zorro.

During a dinner party at the Brookfield family estate, private detective Craig Kennedy relates a story of one of his unsolved murder cases. What Kennedy knows, and the other guests do not, is that the person who was the killer in the unsolved mystery is in the room, and Kennedy makes plans to expose him.