The story of the masked rider in Old California opens as Don Diego de la Vega is returning to California from Spain, where he has been studying for several years.

Finding that Don Torres is in hiding at the Mission, Monastario forces the local Indians into hard labor until the Padre agrees to surrender the fugitive.

After Zorro hides his wounded father in the secret cave, as Don Diego he must divert Captain Monastario and his soldiers who are searching for the old man.

Captain Monastario orders Sergeant Garcia to pretend to have been dishonorably discharged, so that the people of the village will take him into their confidence and reveal Zorro's whereabouts.