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.

The fake Ortega and the magistrado announce they have captured Zorro, and a cart holding a masked man is dragged into the town square. A public unmasking will be held at noon, and Diego fears that an innocent man will be charged with Zorro's "crimes". He also realizes it may all be a trap, so when he dons his costume and rides into the square to free the prisoner, he watches carefully for soldiers.