Vitellia, daughter of the former emperor of Rome who was deposed by the present Emperor Tito’s father, wishes to regain the throne as Tito’s consort. But her hopes are dashed when she learns that Tito plans to marry the Judean princess Berenice. Vitellia persuades Tito’s dearest friend Sesto, who is in love with her, to assassinate the Emperor. But when Vitellia hears that Tito has renounced Berenice in order to grant his subjects’ wish for a Roman empress, her hopes are revived and she calls off the murder plot.
Tito has now chosen Sesto’s sister Servilia as his bride and sends Sesto’s friend Annio to inform Servilia. Annio and Servilia, unbeknownst to Tito, are in love, so they are dejected at this news. Servilia is prepared to obey her Emperor, but she decides to tell him the truth. Touched by Servilia’s honesty, Tito relinquishes her and blesses her betrothal to Annio.
When Vitellia learns of Tito’s plan to marry Servilia, she once again urges Sesto to assassinate the Emperor. Just after Sesto leaves to do the deed, Annio and the guard Publio arrive to escort Vitellia to Tito, who has now chosen her as his Empress. Vitellia regrets sending Sesto on his murderous mission, but it is too late.
While Sesto is still reluctant to carry out the attack, the Capitol is set on fire. It is the agreed sign to overthrow the emperor. Sesto has no choice. While the flames spread, the Roman people express their terror. When Sesto tells Vitellia that Tito is slain, she begs him not to divulge their guilt. All of Rome laments the tragic events.
In the imperial palace, Annio informs Sesto that Tito is still alive; amid the smoke and flames, Sesto had mistaken another man for the Emperor. Sesto confesses his assassination attempt, though he refuses to give any reason. Annio counsels him to confess to Tito and rely upon his mercy. Vitellia urges Sesto to flee, but it is too late: a fellow conspirator has betrayed him, and Publio enters to arrest him.
The Roman people thank the gods for sparing their Emperor. Tito can neither comprehend the motives of the conspirators nor believe that Sesto would betray him, but is then informed that Sesto has admitted his guilt before the Senate. Annio implores Tito to treat Sesto with compassion. The Emperor refuses to sign the death decree until he has given Sesto a chance to explain himself. Sesto admits his crimes to Tito but declines to implicate Vitellia. Tito reluctantly condemns Sesto to death. Left alone, the Emperor is torn between his duty and his feelings, concluding that he can reign only if his power is rooted in love. Annio and Servilia beg Vitellia to use her influence as Tito’s consort to help save Sesto. Vitellia realises that she must admit her guilt rather than win the throne at the cost of Sesto’s life.
At the arena where the conspirators are about to be executed, Tito is about to pardon Sesto when Vitellia arrives and confesses her guilt. Once again mastering his mixed emotions, Tito pardons Vitellia, Sesto, and all of the co-conspirators. As Tito’s subjects praise him, he declares that the gods may take his life on the day when Rome’s well-being is no longer his highest priority.