Ancient Rome, 67 AD.
The Roman forum. Herald announces the sacred will of Nero: on the occasion of the celebrations in honour of Minerva, Nero has ordered the opening of the theatre and the circus. The crowd is jubilant. However, there is a rumour that Christians have reappeared on the outskirts of Rome. The holy procession appears. As the procession passes, the people all fall to their knees; only the Old Man sits motionless on the bench as before. He addresses the people: “Madmen…your gods are but fragments of marble.” With these words he smashes the statue of Diana with his staff. The people are momentarily rooted to the spot to stone the old man. Rattled, Servilia, daughter of Senator Soranus, witnesses the scene from the senator’s house terrace. Suddenly, Tribune Valerius storms into the crowd and prevents the massacre. Servilia is impressed with the young tribune’s beauty and nobility. Valerius looks at Servilia and immediately falls for her.
The baths of Agrippa. Atrocities and brutality of the all-powerful Prefect Tigellinus have outraged the people. Senators led by Paconius are writing a letter to Nero. Egnatius, Senator Soranus’s freedman, is to deliver the letter to Caesar Nero. However, Egnatius turns out to be a traitor. He has hidden Tigellinus behind the secret door and disclosed the senators’ plot to him. Tigellinus wonders what made Egnatius betray their plan. “What passion inspires you? Vengeance, the desire for power, jealousy?” To which Egnatius responds, “It's love!”
Soranus’s house. Servilia sits at a spinning wheel. Soranus informs her that he wants to marry her off to her friend Thrasea. Servilia is in despair as she is in love with Valerius. Thrasea appears and tells Soranus that his step-son Valerius is hopelessly in love with Servilia. Thrasea is ready to reject Servilia and let the two of them be happy. Valerius enters. He can no longer hide his feelings for Servilia. Thrasea and Soranus give the couple their blessing. Valerius and Servilia are beyond happy. However, their bliss is marred by the arrival of a centurion. Soranus and Thrasea are charged with treason against Rome on behalf of Caesar.
Sorceress Locusta's house. Egnatius enters. He knows that Servilia is to come here. Servilia wants to know what will be her father’s fate. Egnatius professes his love to Servilia, who angrily rejects him. Then he tells her that Valerius has fallen at the hands of an assassin and leaves, locking Servilia inside Locusta’s house. Servilia wants to die to be delivered from shame, but Nevolea, Locusta’s Christian slave, frees her. Servilia then becomes a Christian as well.
The temple of Venus. The tribunal is deciding the fate of Soranus and Thrasea. They are accused of treason and sentenced to exile, while Servilia is given over on bail and on probation to Egnatius. At this dark hour, Valerius appears and vetoes the court ruling as a Roman Tribune.
The jubilant crowd surrounds Valerius. He excitedly addresses Servilia, but their happiness is doomed: Servilia is very weak and close to death. Servilia asks Valerius not to take vengeance on his enemies and turn to God instead. She forgives everyone and dies. Shaken, Egnatius and the people prostrate themselves before the one living God.