Federal Agent Gene Autry and his sidekick Frog are sent to Mexico to prevent foreign powers from gaining control of Mexican oil refineries and fomenting revolution among the Mexican people. Gene falls in love with Senorita Dolores but finds he must leave for the island of Palermo, where her uncle, Don Diego, is being prevented from transporting his cattle to market by the foreign agents, who have co-opted Dolores' brother Andreo into joining them. While trying to load cattle by sea into a waiting cargo ship Gene and his men are attacked by Andreo and his revolutionaries, with fatal results.