Talbot uses a phony land grant to rule thirteen million acres, taxing everyone heavily and evicting those who won't pay. The Three Mesquiteers becomes mysterious "night riders" to fight this evil.

In the early 1880's, when a gambler posing as a Spaniard presents a phony land grant dating from the Spanish occupation, which deeds him 13,000,000 acres of ranchland in the Western United States, the government upholds his claim. Setting himself up as a virtual dictator, the phony land baron demands excessive rents for his land and evicts all those unable to pay. Among those evicted are the Three Mesquiteers, Stony Brooke, Tucson Smith and Lullaby Joslin, who appeal to President James Garfield for justice. When Garfield declares that he is powerless to aid the ranchers because the baron's claim has been validated by the court, the Three Mesquiteers become Night Riders to smash the cruel dictatorship of the tyrant. Riding furiously in mask and cape, the Night Riders rob the messengers of the land baron and return the money to the ranchers. Arrested for their crimes, the trio awaits a sentence of death when their friend, Soledad, unearths evidence that the land grant is a forgery. Unfortunately, the evidence reaches Garfield a moment after he is killed by an assassin's bullet. The trio nevertheless is rescued by a friendly sheriff who, realizing that their crimes were committed for the good of the people, loads his firing squad's guns with blanks.