In the third Act Nero accompanied by Tigellinus leads his Pretorian guards to the hiding-place of the Christians.—This he has found out from the confessions of Parthos.—Nero hears Acté's voice singing a Miserere, but commands his guards to conceal themselves.—
The Christians, among them Acté and Marcus, believing themselves safe in the stormy night, at last emerge from the mountain caves, and at a sign from Nero are surrounded by the Pretorian guards.
Nero seizes Acté and tries to win back her love, but Acté remains firm, and she so infuriates her royal lover, that he threatens her with his dagger.—Old Marcus stepping between, only rouses the Emperor's anger to a higher pitch, while Tigellinus denounces the old man as Nero's rival and the cause of Acté's flight. Both are led away as captives with their Christian brethren to Rome.
The last Act takes place on the terrace of the Palatine.
Lovely dances beguile the weary hours for Nero, lying on his couch, a prey to love and hatred. Tigellinus tries to rouse his pride by relating to him the last interview between Marcus and Acté overheard by him.
He describes the old man's exhortations and glowing promises of a better life, and Acté's calm courage and deep faith, and Nero cries: "She must be mine, or she dies!"—At this moment the Christians are heard, greeting Caesar as they pass the palace on their way to death.—Acté is not with them, she is now brought before Nero with Marcus, for whom she implores Nero's pardon.—But it is in vain; Nero falls upon the originator of his woes, and kills him with his own hands.—
In this moment flames are seen leaping up in the streets of Rome.
Tigellinus hurries in, exclaiming that the people accuse their Emperor of having set the city on fire, and already their furious cry is heard: "Death to the red Caesar!"
Beside himself with rage and fear Nero seizes Acté, and throwing her down from the terrace amongst the people, he accuses the Christians of having set fire to the town. Acté perishes a victim to the fury of the people, while Nero cries out: "Burn O Rome, burn, Nero greets Thee!"