Out of a job and at loose ends in the Mexican town of San Rafael, Owen Burke overhears a conversation between two Mexican vaqueros seated at a nearby table in the local cantina. After introducing himself, he learns they work for Don Enrique Hernandez de Allende at a horse ranch some distance south. The don is planning a horse drive to California where his brother-in-law has a ranch. Owen knows those trails and hopes the don might be in need of a guide. Arriving at the don's ranch, he impresses the don and his daughter, Rosa María. However, the ramrod, Chavez, who is suspicious of gringos in general and also guards Rosa María jealously, is not impressed. Despite Chavez's mistrust, Owen is hired as a guide for the drive. After he is ambushed, Owen sets out to find the thieves, recover the horses, and clear his name.