Don Cesar de la Vega, the son of the masked adventurer Zorro, is in Spain to finish his education. His studies are cast aside when a chance meeting with the beautiful Dolores, adopted daughter of Queen Isabella, turns into a whirlwind romance. But Don Sebastian, captain of the Palace Guard, also lusts after the lovely maiden. When the visiting Austrian Archduke is killed by an assassin's bullet, the scheming officer frames Cesar for the murder. With Spain and Austria on the brink of war, the younger de la Vega must take up his famous father's mask and cape to find the real killer.

Though commonplace today, sequels were a rarity during the silent era. In the case of Don Q, Son of Zorro, the film started out as having no connection to star Douglas Fairbanks' earlier hit, The Mark of Zorro (1920). The source material was a 1909 novel, Don Q's Love Story, that actually predated the 1919 publication of the first Zorro story, "The Curse of Capistrano". Once Fairbanks was chosen to star, it was decided to connect the two films by making the protagonist Don Diego de la Vega's son. At the time of its release, Don Q was actually considered a superior film to The Mark of Zorro; this was mostly attributed to the deft direction of Donald Crisp. Though he would later be better known for his performances in classics such as How Green Was My Valley (1941) and National Velvet (1944), during the silent years Crisp had staked out an impressive resume behind the camera, including co-directing Buster Keaton's masterpiece The Navigator (1924). In addition to Fairbanks and Crisp (who also gets to play the film's villain), Don Q features a pair of actors who will be instantly recognizable to audiences: Warner Oland, best known for playing Charlie Chan in a popular series of features from 20th Century Fox, and Mary Astor, immortalized for her role as Brigid O'Shaughnessy in The Maltese Falcon (1941).