Tom Cameron, aka the Lone Rider, and his faithful sidekick, Fuzzy Jones, flee across the Rio Grande to avoid assassination by crooked lawman Deputy Hatfield, only to have the Mexican cops accuse Cameron of being the notorious bandit El Puma. At Hatfield's behest, they are also accused of kidnapping the local mayor's son, and now the pair must prove their innocence and find a way to stop Hatfield's lawless ways.