Returning from Mexico to his native Spain, the noble Marquis, Riccardo di Villa Real, finds himself before a difficult and unexpected situation, as the brother of the deceased Duke of Lusitania, Don Ramon de Castro, has taken possession of the Grand Duchy. Usurping the throne from its legitimate heirs--the Grand Duchess, Giovanna, and her little daughter, Isabella--the treacherous Don Ramon now forces the helpless lady to renounce her royal right; however, an enigmatic man in black known only as the Zorro is out for justice. But, who is this valiant vindicator?