Spain, 1519. Palace of the Duke of Rui Gomez de Silva in Zaragoza. Donja Sol, his niece and bride, is waiting for her lover Hernani - today their fate should be decided. Duanya, hearing a knock on the door, opens and sees instead of Hernani a stranger in a raincoat and hat with wide brim. This is King Don Carlos: inflamed with passion for Don Sol, he wants to know who his rival is. Duenna, having received a purse with gold, hides the king in the closet. Hernani appears. He is gloomy - does he have the right to love Dona Sol? His father was executed by order of the late king, he himself became an exile and a bandit, and the Duke de Silva possesses innumerable titles and wealth. Doña Sol vows to follow Hernani everywhere - even the scaffold. At this moment, Don Carlos, who is tired of sitting in a narrow closet, interrupts the conversation of lovers and playfully invites Don Sol to divide the heart into two. In response, Hernani bares his sword. Unexpectedly for all, the old duke returns to the palace. Don Rui angrily reproaches the niece and young people: in former times no nobleman would dare to desecrate the old man's gray hair, encroaching on the honor of his future wife. Don Carlos, not embarrassed at all, reveals his incognito: extremely important events have occurred - Emperor Maximilian has died, elections are coming and a difficult backstage fight for the throne. The king needs the support of such powerful vassals as the Duke de Silva. The ashamed nobleman asks the king for forgiveness, and Hernani hardly restrains his fury at the sight of his sworn enemy. Left alone, the young man utters a passionate monologue - now he must get even with the king not only for his father, but also for trying to seduce Dona Sol.

The following night, Don Carlos ambushes to stop Doña Sol from escaping Hernani. Eavesdropping on the conversation of lovers, he deduced the agreed sign - three clapping. Doña Sol falls into the trick of the king. Don Carlos promises to make her a duchess, princess, finally, queen and empress. With indignation rejecting the monarch's harassment, the girl calls for help to Hernani, and he appears in time with six dozen loyal mountaineers - now the king is in his full power. The noble robber offers to solve the matter by fight, but Don Carlos arrogantly refuses: yesterday he allowed himself to cross his sword with a stranger, but for a bandit it is too much honor. Hernani, not wanting to be a murderer, releases the king, who, in parting, declares him a merciless war. Doña Sol begs her lover to take her with her, but Hernani cannot accept such a sacrifice: from now on, he is doomed - let Don Do Sol marry his uncle. The girl swears that she will die on the same day as Hernani. The lovers break up, exchanging the first and, perhaps, the last kiss.

Castle of the Duke de Silva in the mountains of Aragon. Donja Sol in white is today her wedding day. Don Rui admires the chaste beauty of his bride, but the girl is not preparing for the wedding, but for death. A page comes in and announces that a certain pilgrim is asking for refuge. The Duke, faithful to the covenants of ancient hospitality, orders to accept the traveler and asks what is heard about the bandits. The page replies that Hernani’s “mountain lion” is over - the king himself is chasing after him, and a reward of a thousand ecu has been awarded for his head. Hernani appears in a pilgrim costume: when he sees Don Sol in a wedding dress, he calls his name in a thunderous voice - let him be betrayed to the king. Don Rui replies that no one in the castle dares to betray a guest. The old man leaves to give the necessary orders for the defense of the castle, and there is a stormy explanation between the lovers: the young man accuses Don Sol of treason - when he sees the dagger she has prepared for her wedding night, she falls into repentance. The returning duke catches the bride in the arms of Hernani. Shocked by such treachery, he compares Hernani with Judas. The young man begs to kill him alone, sparing the innocent doña Sol. At this moment, Don Carlos appears with his army in front of the castle. The duke hides his opponent in the cache behind the picture and goes out to meet the king. He demands to extradite the rebel. Instead of an answer, Don Rui shows portraits of his ancestors, listing the exploits of each - no one dares say about the last of the dukes that he is a traitor. Enraged, the king threatens him with all kinds of punishments, but at the sight of a dona Sol changes his anger to mercy - he is ready to spare the duke by taking his bride hostage. When the king retires with his prey, the old man releases Hernani. The young man begs not to kill him now - he must take revenge on don Carlos. Having handed over the hunting horn to the duke, Hernani vows to give his life when don Rui demands it.

Aachen. The tomb of Charles the Great includes the king, accompanied by don Ricardo de Rojas. At night, conspirators — German princes and Spanish grandees who vowed to kill Don Carlos — would gather in the crypt. Recently, an old man and a young man appeared among them, who stand out for their determination. The king coldly replies that all the traitors are waiting for the scaffold - if only to become the emperor! At this hour, electors are conferring. The bell will announce their decision: one blow means that the Duke of Saxony is elected, two - Francis I defeats, three - Don Carlos becomes emperor. The king, having sent Don Ricardo, approaches the tomb of Charles: appealing to the shadow of the powerful emperor, he begs to instruct him - how to cope with the monstrous burden of power? Hearing the steps of his killers, Don Carlos is hiding in the tomb. The conspirators are drawing lots - one of them must sacrifice himself and inflict a mortal blow. To the great joy of Hernani, this honor falls to him. Don Rui begs the opponent to yield, but Hernani is adamant. At this moment the bell beats. At the third blow, Don Carlos emerges from the tomb - now Emperor Charles V. From all sides, people close to him rush to him, and Karl asks to bring Don Sol - maybe the title of Caesar will captivate her heart? The emperor orders only the dukes and counts to be taken into custody - the other conspirators are not worthy of his revenge. Hernani proudly comes forward: now he does not need to hide his name - Prince Juan of Aragon, the Duke of Segorba and Cardona has the right to climb the scaffold. Doña Sol kneels before don Carlos. Having risen above insignificant passions, the emperor forgives everyone and agrees to the marriage of Dona Sol with Hernani, to whom he returns the lost titles. The former robber renounces his former enmity - only love remained in his heart. He does not notice the hating gaze of the old duke.

Palace of the Prince of Aragon in Zaragoza. Hernani and Dona Sol have just been married. The guests lively discuss the miraculous transformation of the robber into a Spanish grandeur. Everywhere praises are given to the emperor and the young beautiful couple. A gloomy masked figure stands out against the background of general fun - no one knows who this person is, but death blows from him. Happy newlyweds appear: everyone congratulates them and hurries to leave alone. Hernani and Dona Sol are immensely happy. In the midst of the most fervent confessions, the sound of a hunting horn is heard. Hernani shudders and turns pale: having told his wife that he had an old wound, he sends her for a healing balm. A masked man comes in - it's Don Rui Gomez came for Hernani. Hernani picks up the goblet of poison, and at that moment Dona Sol returns. Seeing the old man, she instantly realizes the danger hanging over her husband. Don Rui reminds the young man of the oath, Don Sol calls for love. After ascertaining the futility of supplication and threats, she grabs the goblet and takes half a drink - the rest goes to Hernani. Lovers hug and weakening tongue bless the sky for this last kiss. Seeing the terrible work of his hands, don Rui kills himself. The curtain.