In 1910, during the Mexican Revolution, the Federal troops of unpopular Mexican President Porfirio Díaz wreak havoc in the countryside eliminating all resistance. The supporters of the Opposition politician Francisco Madero organize armed resistance against Diaz but they need money and weapons. When Federal troops devastate a Mexican village that sheltered fugitive rebel army leader Durango, the soldiers kill most inhabitants but villager Felipe Rivera escapes. He illegally crosses the border into the United States at El Paso, Texas. In El Paso, Felipe seeks help from a Mexican printing shop that prints revolutionary sheets meant to familiarize Americans with the plight of the Mexican rebels. The printing shop hires Felipe as a helper. In order to support himself, Felipe becomes a prize-fighter. Some of the money he wins also goes to the printing shop as a contribution to the cause. Later, Felipe meets a boxing promoter who gradually brings Felipe to the forefront of local boxing league. The printing shop owner, who also is a revolutionary leader, sends Felipe on occasional errands to Mexico. During such an errand, Felipe must go back to Mexico with an important message for rebel leader Durango. In Mexico, Felipe learns that Durango has been captured and imprisoned by the Federal troops. Felipe devises a plan to help rescue Durango from an army prison. Durango tells Felipe that he appreciates the propaganda work done in El Paso by Felipe and his friends but also tells him that weapons are needed by Mexico more than propaganda. Felipe returns to El Paso determined to fund-raise the five thousand dollars needed to buy 1000 old surplus rifles from the U.S. Army. The only way he can raise this huge sum is by competing in major boxing events. Boxing gymnasium owner and boxing promoter Roberts promises Felipe a main event fight against the current boxing champion, in a winner-take-all match. Although much smaller and less experienced than his opponent, Felipe is driven by the enthusiasm of helping the Mexican Revolution with the much needed weapons. He is also motivated by feelings of revenge against the Mexican Federal troops who killed his family and all the inhabitants of his native village.