The action takes place in Rome, in the house of Lattanzio, first 'buffo' and head of a company of opera singers.

ACT ONE

Composer Bequadro is rehearsing at the harpsichord, for librettist Vulcano, an aria of his new opera. They are interrupted first by second singer Fulgenzia, who complains about her aria, then, by bass Biscaglino, who asks that his part be transposed in a different tonality, and finally by Ascanio, the prompter, and the choir, who have come to rehearse their part. Enters Lattanzio, frustrated by his job as impresario. His irritation mounts considerably when Vulcano brings him his new libretto, a mythological and half-comical text entitled Penelope tra i Porci (Penelope among the Swines). Lattanzio, furious, moves away and stumbles upon his wife Aurelia, first singer of the company, who is flirting with Colonel Ortenzio, making him believe that she is a countess and a widow anxious to remarry. Lattanzio approaches them and is about to make a scene of jealousy when Aurelia anticipates him by introducing him as Count Ascrubale. There follows a peculiar conversation by which we understand that Colonel Ortenzio is the uncle of young Eduardo who, against the wishes of his noble family, loves and is loved by Eugenia, Lattanzio's ward. Ortenzio has come to Rome in order to prevent the marriage between his nephew and a singer, which would stain the honour of his noble lineage. Aurelia convinces her jealous husband that her flirting with Ortenzio is just part of the plan she has devised to get the two lovers married; plan that is going to be carried out that very evening, during a party that will be held after the staging of Carnevale di Venezia, and that will be attended by the whole cast in costume. Colonel Ortenzio returns in civilian clothes, ready for the party and, finding himself alone with Lattanzio, confides to him that he has fallen in love with the countess and that he hopes she will agree to marry him. As the various members of the company arrive, they are introduced to him: Baron Bat, Duke of the Green Beech Duchess Beatrice, Duke Belisario ... but it is time for them to go on stage and, with a pretext, they leave.

ACT TWO

Left alone with Eduardo, Ortenzio confirms his strong opposition to his marrying Eugenia. Eduardo leaves. Enters Fiordelisa, a singer looking for an engagement, who mistakes the Colonel for Lattanzio, while the Colonel mistakes her for his nephew's sweetheart. The misunderstanding is soon revealed when the Colonel finds out, through Fordelisa, about Lattanzio's real identity. Meanwhile the opera has ended, and the performers are back commenting the evening's fiasco and blaming each other for it. Suddenly loud knocking is heard at the door: it is the Colonel, in a wild rage. Aurelia tries to calm him down; she admits to being a singer but insists that she is a widow and tells him that she wishes to marry him, on condition that their wedding be celebrated after the one between Eugenia and Eduardo. Madly in love, the Colonel surrenders and accepts. But after the knot between nephew and ward has been tied, Lattanzio reveals to him that he is Aurelia's legitimate husband, the charming 'widow's' alive and kicking spouse. The plan has succeeded and love has, once again, triumphed.