The noise attracts the attention of Adrian, heir of the Colonna family, and when he perceives that the would-be kidnappers wear the arms and livery of the Orsini, his hereditary foes, he seizes with joyful alacrity the opportunity to fight, and pounces upon them with all his escort.  A confused street skirmish ensues, in the course of which Adrian rescues the beautiful maiden, whom he recognises as Irene, Rienzi’s only sister.  Attracted by the brawl, the people crowd around the combatants, cheering and deriding them with discordant cries, and becoming so excited that they refuse to disperse when the Pope’s Legate appears and timidly implores them to keep the peace.

The tumult has reached a climax when Rienzi suddenly comes upon the scene, and authoritatively reminds his adherents that they have sworn to respect the law and the Church, and bids them withdraw.  His words, received with enthusiastic cries of approbation by the people, are, however, scorned by the barons, who would fain continue the strife, but are forced to desist.  Anxious to renew hostilities as soon as possible, and to decide the question of supremacy by the force of arms, the irate noblemen then and there appoint a time and place for a general encounter outside the city gates on the morrow, when they reluctantly disperse.

The appointment has been overheard by Rienzi, who, urged by the Legate of the Pope and by the clamours of the people to strike a decisive blow, decides to close the gates upon the nobles on the morrow, and to allow none to re-enter the city until they have taken a solemn oath to keep the peace and respect the law.  In an impassioned discourse Rienzi then urges the people to uphold him now that the decisive moment has come, and to rally promptly around him at the sound of his trumpet, which will peal forth on the morrow to proclaim the freedom of Rome.

When they have all gone in obedience to his command, the Tribune, for such is the dignity which the people have conferred upon their champion Rienzi, turns toward the girl, the innocent cause of all the uproar, and perceives for the first time that it is his own sister Irene.  Adrian is bending anxiously over her fainting form; but as soon as she recovers her senses she hastens to inform her brother that he saved her from Orsini’s shameful attempt, and bespeaks his fervent thanks for her young protector.

It is then only that the Tribune realises that a Colonna, one of his bitterest foes, and one of the most influential among the hated barons, has overheard his instructions to his adherents, and can defeat his most secret and long cherished plans.  Suddenly, however, he remembers that in youth he and Adrian often played together, and, counting upon the young nobleman’s deep sense of honour, which he had frequently tested in the past, he passionately adjures him to show himself a true Roman and help him to save his unhappy country.  Irene fervently joins in this appeal, and such is the influence of her beauty and distress that Adrian, who is very patriotic and who has long wished to see the city resume its former splendour, gladly consents to lend his aid.