Irish immigrant Michael Callahan gets the gold fever and stakes a claim in California. Just when persistence and ingenuity finally payoff, he is jumped by thieves intent upon taking his gold and his life. Michael is saved by the Mexican, Joaquin Murieta with whom he strikes up a friendship. The friendship is quite unusual and the Irishman becomes known as the Gringo Amigo. But hatred by Anglos, and the death of his family, sends Murieta on a bloody mission of vengeance that inflames the countryside. Murieta becomes the most wanted man in the state. Perhaps the only man that can save him is the loyal Gringo Amigo...