In Venice, 24 farm girls declare their passions for the handsome gondolier brothers Marco and Giuseppe Palmieri, who blindfold themselves in order to choose their brides fairly. Eventually, Giuseppe picks Tessa, and Marco picks Gianetta, and all four head to church for a double wedding.

The Duke and Duchess of Plaza-Toro, along with their daughter Casilda, arrive from Spain to meet with Don Alhambra del Bolero, the Grand Inquisitor. While their drummer Luiz departs to announce the Duke’s arrival, the Duke and Duchess reveal to their daughter a secret they have kept for 20 years: when she was just six months old, she was married to the infant son of the King of Barataria, who was spirited away to Venice by the Grand Inquisitor, and is now King himself following his father’s demise in an insurrection. Casilda is therefore now Queen of Barataria, and her parents have brought her to Venice so that she can meet her husband. Secretly in love with Luiz, Casilda resigns herself to a life apart from him.

The Grand Inquisitor arrives, and explains that the baby Prince of Barataria was raised by the Venetian gondolier Baptisto Palmieri, who had a son of a similar age and quickly forgot which was which. The two boys – Marco and Giuseppe Palmieri – grew up to become gondoliers themselves. Only the nurse Inez who looked after them (and who also happens to be Luiz’s mother) knows which is which, but she is now living with a brigand in the mountains. The Grand Inquisitor sends Luiz to find her.

When Marco and Giuseppe arrive with their wives, Don Alhambra explains that one of them is the King of Barataria, but nobody knows which one. Despite their Republican beliefs, the ‘brothers’ are delighted, and agree to travel to Barataria at once, acting together until the real King can be identified. Don Alhambra advises their wives that they cannot be admitted to Barataria until the King has been declared – neglecting to mention that the real King is already married to Casilda.

In Barataria, Marco and Giuseppe are enjoying splendid lives, but nonetheless miss their wives. Themselves struggling to endure the separation, the ladies soon arrive from Venice, and all celebrate with a grand ball.

Don Alhambra arrives at the palace to discover that Marco and Guiseppe have promoted everyone to the nobility, and breaks the news that the true King was married to Casilda as a baby – and is therefore an inadvertent bigamist. The gondoliers’ wives are distraught to discover that neither of them will be Queen.

The Duke and Duchess of Plaza-Toro arrive with Casilda, and, shocked by the lack of pomp and ceremony to welcome them, set about educating Marco and Giuseppe in proper royal behavior. The two erstwhile gondoliers are left alone with Casilda, who promises to be a loyal wife to one of them, and when their other wives arrive, all five sing of their strange predicament.

Don Alhambra arrives with the nurse Inez who knows the King’s true identity. She confesses that when the Grand Inquisitor arrived to steal the baby Prince away, she substituted her own young son, keeping the true Prince under her own guard. Thus it is neither Marco nor Giuseppe who is King, but Luiz – and Casilda discovers that she is already married to the man she loves. The two gondoliers, though disappointed not to be King, return to Venice happily with their wives.