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.

It is a calm morning in Spanish California, and Sergeant Dimetrio Lopez Garcia is putting up posters, with another soldier, which are asking for reward money for Don Ignacio Torres and the now famous Zorro.

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 failing in his attempt to sneak food to the fugitive in the Mission where Captain Monastario has laid siege, Zorro tries to scare the soldiers away by spreading a rumor about the mad monk who supposedly haunts the place.

Learning that a group of disgruntled landowners plan to seize the cuartel and free the political prisoners, Captain Monastario sets a trap to capture them, including Zorro's father Don Alejandro.

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.