Shrove Monday, evening; Balducci’s house
The Pope’s Treasurer Balducci is dissatisfied that the Pope has invited the Florentine jeweller Benvenuto Cellini to carve a statue of Perseus when the Pontiff has the services of the sculptor Fieramosca, to whom Balducci wishes to marry his daughter Teresa. Balducci is also furious with Cellini as the latter does not hide his admiration for Teresa and sings romantic songs beneath her window at night. Understanding that she cannot rely on her father’s blessing, Teresa agrees to Cellini’s proposal to elope on Carnival night. Fieramosca overhears the lovers discussing their plot and resolves to stop them.
Shrove Tuesday, evening; the Piazza Colonna
In a taverna on the Piazza Colonna, Cellini is feasting with his friends and observing the preparations of the actors in Cassandro’s wandering troupe for the Carnival performance. But there is no more money for wine and the innkeeper demands payment. Fortunately Cellini’s devoted student Ascanio arrives, bringing the advance fee for the statue of Perseus. It is true that this fee is niggardly as Balducci, the Papal Treasurer, is known as a notorious miser throughout Rome. The friends resolve to persuade the actors to mock the Treasurer in the satirical pantomime King Midas or the Ass’s Ears. Meanwhile, Fieramosca, having called on the bandit Pompeo to help, considers how to prevent Cellini eloping with Teresa.
The audience assembles for the performance. Among them are Balducci, Teresa and Cellini and his student Ascanio dressed in monks’ cowls. Balducci, enraged at the parody of himself he has seen in the performance, threatens the actors that he will denounce them to the Pope. In the emerging chaos Teresa wishes to flee with Cellini but sees four monks instead of two. The second two Fieramosca and Pompeo. A dispute ensues and Cellini kills Pompeo. The sculptor manages to conceal himself and Fieramosca is arrested.
Scene 1. Ash Wednesday (the first day of Lent), dawn; Cellini’s studio
A religious procession passes by the windows of Cellini’s studio. Teresa and Ascanio are praying for his salvation. A moment later, to the joy of both, Cellini appears. He has decided to abandon work on the statue and flee with Teresa to Florence immediately. But the lovers’ path is barred by Balducci and Fieramosca, who has been released from prison. The Treasurer demands that Teresa marry Fieramosca. Cellini threatens to murder Fieramosca if the latter so much as touches Teresa. The dispute is interrupted by the arrival of the Pope who has come to see Cellini’s work. Observing that the statue of Perseus is not ready the Pope declares that he will give the commission to another sculptor. In despair Cellini wants to smash the plaster model, but the Pope gives him until the evening to complete it and presents an ultimatum: if Perseus is finished by nightfall the Pope will pardon all his sins and he will be permitted to marry Teresa. If not, he will be executed.
Scene 2. Evening the same day; the smelting house of Cellini’s studio
Ascanio is impatiently awaiting his teacher’s “bronze masterpiece”. But Cellini despairs: at every turn he encounters more and more obstacles. Fieramosca appears and challenges him to a duel. Teresa tries to prevent her beloved going to the duel, but Cellini assures her there is no danger. He departs, and immediately the studio is overrun by Cellini’s workers. They are on strike as they have not received their wages for a long time. But when Fieramosca appears again to bribe them and make them work for him (the duel was a mere pretence to get Cellini out of his house) their devotion to their master takes the upper hand. They are just about to throw the schemer into the furnace when Cellini returns. Frightened to death, Fieramosca agrees to work for his former rival. Pope Clement and Balducci arrive. Work on the statue commences.
In the smelting process, however, it emerges that there is insufficient metal. Cellini then throws all of the jewellery he has previously made into the furnace. When the mould is broken all are faced with Perseus Holding Medusa’s Head. All are delighted. The sculptor has been saved and he receives Teresa’s hand in marriage.