After escaping death at the hands of a Mexican army firing squad, Gil Farra, a renegade U.S. Army officer, George Bird, a slap happy ex-boxer, and Sierra, a handsome caballero, begin a long trek to the U.S. border. While stopping at a waterhole, they meet little Mary Elizabeth "Squib" Clayborn and her ailing grandfather, who have been driven from the town of Santa Marta for publishing the local newspaper. The trio decide to accompany Squib and her grandfather back to Santa Marta, where they see the eerily deserted Santa Marta hacienda looming over the town square. Inside, they meet the owner, Colonel Lewis Rebstock, who has just returned from Europe to live in the seclusion of his estate. When Clayborn is murdered, the trio decide to stay in town to help Squib. When another murder is committed, however, they are accused of the crime, and a clever Gil convinces their accusers that George is a famous lawman, thus prompting the townfolk to appoint him marshal of Santa Marta. The new marshal is soon called upon to keep the peace when renegade Tod Shelby rides into town and kills a man. Swinging into action, the threesome apprehend Shelby and his men and throw them in jail. That night, Gil, Sierra and George join Squib in celebrating her birthday. Also at the party are Mr. Prout, the newspaper publisher; Sharon McCloud, the pretty town shopkeeper; and Johnny Cash, a windmill builder whose efforts are continually being sabotaged. As Gil and Johnny vie for Sharon's attentions, Shelby kills his guard and escapes from jail. Gil and the others undertake a search for the fugitives. Meanwhile, back at the newspaper office, Squib and Prout realize that Rebstock must be behind the lawlessness that has been plaguing the town. As they print an editorial denouncing him, Rebstock suddenly appears, shoots Squib and sets fire to the office. Rushing to the burning building, the trio find Squib's body with the editorial accusing Rebstock. They storm Rebstock's hacienda, where he admits to committing the crimes as a way of defending himself against the encroachment of settlers. In a pitched gun battle, the three eliminate Rebstock and his gang, thus restoring law and order to Santa Marta. After witnessing the marriage of Sharon and Johnny, Gil, Sierra and George ride off to California.