Act 1
A room in Palestrina's house, Rome, around 1560
(Scene 1) Palestrina's student Silla is trying over a secular lyric he has written, and planning to make a new life in Florence, where he hopes to find his own voice as a singer and songwriter. Rome clings to its old-fashioned polyphony as closely as it defends its religion. (2) Ighino and Silla discuss their singing: Silla thinks a singer should stand alone, but Ighino thinks that real strength lies subordinating the individual self to the larger complex idea. He is sad because his father has lost heart: fame made others jealous, his marriage led the Pope to dismiss him, and his wife died knowing this. Since then Palestrina has written nothing. Silla sings to him his new song. (3) Cardinal Borromeo is visiting Palestrina to explain that, because of growing secularism, the Pope plans to banish polyphony from the Mass and other offices, to burn the polyphonic masterpieces, and to revert entirely to the Gregorian chant. Emperor Ferdinand I hopes that a new polyphonic Mass can be written which will appease his fears. Borromeo wants Palestrina to undertake this, but, lacking the spirit, he refuses, and Borromeo leaves in anger. (4) Palestrina ponders his loss of faith and the weakness of love. In his despair, spirits of the great music-masters of previous ages appear and surround him. (5) The spirits tell Palestrina he belongs to their elect and must fulfil the task. He protests that in the modern consciousness, art cannot thrive. The spirits reply that this is his earthly mission: he must bring the light to his generation. They vanish. (6) In the darkness of his room angels begin to appear, singing the Mass, and his dead wife's spirit approaches. Not seeing them, Palestrina feels a surge of joy as the walls and ceiling open up to celestial light full of glory and angels, who sing the Gloria. In a creative transport Palestrina's pen is inspired, and as it all fades, he sinks exhausted to sleep, surrounded by sheets of music strewn all around. (7) Silla and Ighino enter while he sleeps, and find the music: it is a complete Mass, written in one night. Ighino rejoices, but Silla is sceptical.

Act 2
The Great Hall in Cardinal Madruscht's Palace in Trent
(Scene 1) Bishop Severolus and the Papal legate Novagerio prepare the hall for the final General Congress of the Council of Trent. The Cardinal of Lorraine (who has reached compromise with the Pope) and Count Luna, representative of the King of Spain (favouring Protestantism) must be seated equally and without precedence. (2) Cardinal Madruscht and Novagerio discuss the coming decision while awaiting the delegates, and they greet Borromeo. (3) While delegates arrive, Borromeo and Novagerio talk politics: Emperor Ferdinand and his son Maximilian plan to have dominion of the Catholic world (including Germany) from the throne of Spain, in union with the Kingship of Rome, which is offered to Maximilian even though he is secretly inclined to Lutheranism. But the Pope will preserve dogma by the interpretation of imperial decrees. Borromeo explains that Palestrina has refused the commission for the new polyphonic Mass. Novagerio insists that Palestrina must be forced into subordination, or be crushed. (4) Cardinal Madruscht deplores Lorraine's compromise with Rome, and urges the Cardinal of Prague to stand fast for doctrinal Reforms. The Spanish arrive and look scornfully at the Italians and the Bishop of Budoja. Morone, the other papal legate, arrives and the Council begins. (5) Morone opens the meeting hoping for unity of purpose between Emperor, Pope and Princes. The question of the polyphonic Mass is raised, but Borromeo tells them it is unfinished. The issue of the vernacular Mass and breviary arises, but then Count Luna and Cardinal of Lorraine dispute precedence, and Budoja disrupts proceedings to deflect Count Luna's case. Chaos breaks out: the meeting is adjourned till the afternoon, when everything must be resolved. The delegates disperse. (6) Lorraine protests to Morone that he should have precedence, but Morone is angry that he has provoked Count Luna. Novagerio appeals to Lorraine to consider the interests of the Pope. Badoja makes himself objectionable. (7) The Spanish servants, and a group of German and Italian servants, shout abuse at each other and a battle with daggers ensues. Cardinal Madruscht appears with a troop of soldiers, and commands them to shoot to kill. A volley is fired, and many fall dead and wounded: all the survivors are seized and carried off for torture.

Act 3
Palestrina's house in Rome, as in the First Act.
(Scene 1) Palestrina, aged and very tired, waits in his room with Ighino and some choristers. Borromeo imprisoned him for refusing the commission, but Ighino handed the music of the Mass over to save his father from the hangman. Now it is being sung before the Pope. Ighino begs his father to reawaken to life and to embrace the son who loves him. Suddenly the voices of singers from the Papal chapel are heard from the street singing 'Evviva Palestrina, the Saviour of Music!' (2) Papal singers come into the room, saying how greatly the Mass has pleased everyone. Pope Pius IV himself enters with eight Cardinals (including Borromeo), Palestrina kneels, and the Pope asks him to return and lead the Sistine Choir until the end of his days. Then they leave, but Borromeo remains and prostrates himself in tears, begging Palestrina's forgiveness. Palestrina raises him up, kisses him on the cheek and embraces him, for both are shattered vessels that must be filled with the breath of love. Borromeo, much chastened, departs: Ighino embraces his father, and asks if he will now be happy. Silla has gone to Florence, but Ighino will remain: in joy the boy rushes out into the street. Palestrina looks at his wife's portrait, and with an expression of devotion to God sits at the organ and begins to play.