Spain, 1519. Palace of the Duke of Rui Gomez de Silva in Zaragoza. Late evening. The old man is not at home. Dona Sol, his niece and bride, is waiting for her lover Ernani – today their destiny must be decided. Duenna, hearing a knock on the door, opens and sees instead of Ernani a stranger in a raincoat and a hat with wide margins. It’s King Don Carlos: flushing with a passion for Donae Sol, he wants to know who his rival is. Duenna, having received a purse with gold, hides the king in the closet. Appears Hernani. 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 thug, and the Duke of Silva has innumerable titles and riches. Doña Sol solves to follow Hernani everywhere – even on the scaffold. At this point, Don Carlos, who was tired of sitting in a narrow closet, interrupts the conversation of lovers and playfully offers Doña Sol to share the heart for two. In response, Ernani reveals his sword. Unexpectedly, the old duke returns to the palace. Don Ruy angrily reproaches his 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: there were extremely important events – the Emperor Maximilian died, elections are coming and a complex behind-the-scenes struggle for the throne. The king needs the support of such powerful vassals as the Duke of Silva. The ashamed noble asks the king for forgiveness, and Ernani with difficulty restrains his anger at the sight of his sworn enemy. Left alone, the young man pronounces a passionate monologue – now he must get even with the king not only for his father,
The next night, Don Carlos arranges an ambush to prevent the flight of Dona Sol from Hernani. Overhearing the conversation of the lovers, he found out an agreed sign – three clapping hands. Doña Sol is caught in the king’s ploy. Don Carlos promises to make her a duchess, a princess, finally a queen and an empress. With indignation rejecting the harassment of the monarch, the girl appeals for help to Hernani, and he appears on time with six dozens of faithful mountaineers – now the king in his full power. A noble robber proposes to decide the matter by dueling, but Don Carlos arrogantly refuses: yesterday he allowed himself to cross the sword with a stranger, but for a gangster it is too great honor. Ernani, not wanting to be a murderer, lets go of the king, and the latter bids him farewell to a merciless war. Doña Sol solicits the beloved to take her with him, But Hernani can not accept such a sacrifice: from now on he is doomed – let Dona Sol marry his uncle. The girl swears she will die on the same day as Hernani. Lovers parted, exchanging the first and, perhaps, the last kiss.
Castle of the Duke of Silva in the mountains of Aragon. Dona Sol in white – today is the day of her wedding. Don Rui admires the chaste beauty of his bride, but the girl is preparing not to a wedding, but to death. The page enters and announces that a pilgrim asks for shelter. The Duke, faithful to the behests of ancient hospitality, orders to take the traveler and asks what is heard about the bandits. The page responds that the “mountain lion” of Ernani is over – the king himself is chasing after him, and a reward of a thousand crowns is assigned for his head. Appears Hernani in the costume of a pilgrim: seeing Don Solja in a wedding dress, he thunderously calls his name – let him be handed over to the king. Don Ruy replies that no one in the castle dares to give out a guest. The old man leaves to give the necessary orders for the defense of the castle, and between the lovers there is a rapid explanation: the young man accuses Sol’s of treason of treachery – when she sees the dagger she prepared for her wedding night, she falls into remorse. The returned duke finds the bride in the arms of Hernani. Shocked by such perfidy, he compares Ernani with Judas. A young man... begs to kill him alone, sparing the innocent dona Sol. At this moment, Don Carlos appears with his army in front of the castle. The Duke hides his rival in a hiding place behind the painting and goes out to meet the king. He demands to extradite the rebel. Instead of answering, Don Rui shows the portraits of his ancestors, enumerating the exploits of everyone, – no one dares to say about the last of the dukes that he is a traitor. The furious king threatens him with all sorts of punishments, but at the sight of the doña Sol changes anger to mercy – he is ready to spare the duke by taking his bride as 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. Handing the duke his hunting horn, Ernani swears to give his life when don Rui demands it.
Aachen. In the tomb of Charlemagne is the king, accompanied by Don Ricardo de Rojas. At night, the conspirators – German princes and Spanish grandees, vowed to kill Don Carlos will gather in the crypt. Recently among them appeared an old man and a young man who stand out with their determination. The King responds coldly that the scaffold is waiting for all the traitors – just to become an emperor! At this hour, electors are conferred. Their decision will be announced by the bell: one blow means that the Duke of Saxony is elected, two are defeated by Francis I, three – Don Carlos becomes the emperor. The king, sending Don Ricardo, approaches the tomb of Charles: appealing to the shadow of a powerful emperor, he begs to instruct him – how to cope with the monstrous burden of power? Hearing the steps of his killers, Don Carlos hides in the tomb. The conspirators draw lots – one of them must sacrifice himself and cause a fatal blow. To the great joy of Hernani, this honor falls to him. Don Rui begs the opponent to give in, but Ernani is adamant. At this moment, the bell beats. On the third blow from the tomb comes Don Carlos – henceforth the Emperor Charles V. On all sides to him rushing attendants, and Karl asks to bring Don Sol – perhaps the title of Caesar will captivate her heart? The emperor orders only dukes and counts to be taken into custody – the other conspirators are unworthy of his revenge. Hernani proudly comes forward: now he does not need to hide his name – Prince Juan Aragon, Duke of Segorba and Cardona has the right to ascend the scaffold. Doña Sol rises to her knees in front of Don Carlos. Rising above insignificant passions, the emperor forgives all and gives consent to the marriage of Dona Sol with Hernani, to which the lost titles are returned. The former robber renounces the previous enmity – only love remains in his heart. He does not notice the hateful gaze of the old duke.
Palace of the Prince of Aragon in Zaragoza. Late evening. Hernani and Dona Sol were just married. Guests are animatedly discussing the miraculous transformation of the robber into a Spanish grandee. Everywhere there are praises to the emperor and the young beautiful couple. Against the backdrop of the general fun, a gloomy figure in a mask stands out – no one knows who this person is, but it’s death from him. Appear happy honeymooners: everyone congratulates them and hasten to leave some. Ernani and Dona Sol are immensely happy. In the midst of the most ardent confessions, the sound of a hunting horn is heard. Ernani shudders and turns pale: having told his wife that he had an old wound, he sends it to the healing balm. The person in the mask enters – this is Don Rui Gomez came for Hernani. Ernani takes the goblet with poison, and at that moment Dona Sol returns. Seeing the old man, she instantly understands, what danger hung over her husband. Don Rui reminds a young man of his oath, Dona Sol appeals to love. Convinced of the futility of pleading and threats, she snatches the goblet and sips to half – the rest goes to Ernani. Lovers embrace and weaken the sky for this last kiss. Seeing the terrible work of their hands, Don Ruy kills himself. A curtain.