In the hall of a hotel near the Lodi theatre, the serious opera Romolo ed Ersilia is being rehearsed (Introduction: “Cori, attenti; e a tempo entrate”). Also present besides the singers and chorus are the composer, the librettist and the impresario. Daria, the prima donna, is accompanied by her husband Procolo, and the company is completed by the Tenor, the Musician and Luigia, the seconda donna.

Each of these figures would like to spotlight their own role by appealing to ‘theatrical conveniences’, namely the customs and laws governing a production. In particular, the Tenor, the Musician and the seconda donna complain of the excessive importance accorded to the prima donna. For her part, in a fit of pique she questions the choices of librettists and music.

Suddenly Agata, the overbearing and intrusive mother of the seconda donna, bursts onto the scene, demanding a rondo to be specially written for her daughter (Cavatina “Lazzarune, scauzacane”) and dictating its style to the Music Master. Meanwhile, no sooner has the Poet begun to read the programme than each singer presents his or her complaints. They all want to see their titles given more prominence and in the right order.

The tension rises to a peak when Mamm’Agata demands a duet for her daughter with the prima donna, who refuses for fear of lowering herself to the rank of second. Agata and Daria argue and angrily insult each other (“Ch’io canti un duetto?”). The Tenor, who has scented the atmosphere, threatens to walk out, while Procolo declares that he is ready to replace him. Agata, too, offers to substitute the Musician, who in the meantime has vanished. The rehearsal starts with the Tenor (Trio “Per me non trofe calma”). Faced however with the prospect of having to sing a duet with Mamm’Agata, who has proved an excruciatingly bad singer, he heads for the exit.