The story relates the adventure of a young girl, Francesca, whose father is a fencing master. He has educated her as a boy, teaching her fencing among other manly accomplishments. She takes his place as master-at-arms. She loves Fortunio, rightful heir to the throne of Milan. He believes her to be a boy. When the usurping duke and his household magician scheme to remove Fortunio, Francesca accompanies him. Fortunio has been in love with the young Countess Filippa, while the Marchesa Goldoni, a young widow, is enamored of the boyish graces of Francesca. The comedy is supplied by the bankrupt Duke of Milan, who has a private astrologer to whom such fabulous sums have been paid for horoscopes that the ducal exchequer is depleted. The Duke has mortgaged his palace, one room at a time, to the money lenders of Milan. Subsequently the Duke employs a band of Venetian bravos to suppress Fortunio, the bravos being a regularly organized stock company conducted in a strictly business-like manner. The first act ends with the departure of Fortunio and Francesca to Venice on a political mission.
The second act shows Venice by moonlight, and the finale represents the historic ceremony of the marriage with the Adriatic, an elaborate stage pageant, historically accurate, the Bucentaur or golden barge being an exact copy of the original royal craft. Filippa is sent to Venice to be married, but Fortunio plans to elope with her and trusts Francesca with the secret. In her jealousy of Fortunio Francesca betrays the plan to his rival, Guido, who carries off Filippa. Discovering Francesca's treachery, Fortunio provokes a duel with her, wounds the supposed youth, and compels her to reveal her identity. Fortunio is arrested by the Duke, and is about to be taken to a Venetian dungeon when Francesca declares herself to be the real traitor and is led away in his place.
In the third act Francesca escapes from prison in a woman's dress provided by the Marchesa, who still believes her to be a man. Filippa gives a fete at which she is to announce the name of her future husband. Fortunio has an appointment with her, but Francesca, provided with a mask and domino like Filippa's, takes the place of the countess, and learns from Fortunio that he really loves Francesca and not Filippa. The Duke and Pasquino are driven from Milan, while Fortunio is restored to the throne of his ancestors.