Nine months after the showdown at Elephant Butte Lake, United States Marshal Jake Keller and Professor Kirby Higgstrom are invited to a feast in the Mexican village of San Ignacio after assisting the authorities in round up the region's most notorious outlaw, Juan Javier Lopez.
They are drugged and end up in Mexico City, where they are charged with murdering the peasants of San Ignacio.
They escape and end up in the village of Tlaxcala, where they team up with village matriarch, Doña Isabella Escobar Villalobos, her brothers and a mysterious vigilante named La Esperanza to clear their names.
They uncover a vast conspiracy by Lopez and his brother, Mexican dictator Jose Alejandro Lopez, the surviving members of the Blackheart Gang, along with top officials in the New Mexico territorial government.
Keller and Higgstrom also learn that Lionel Hayes and his rogue Riverton agents were a part of the conspiracy until Keller took them down in a shootout at Elephant Butte Lake.
If the Lopez brothers and the Blackheart gang succeed, they will change the course of history for Mexico and the United States.