A band of outlaws while away the time. Ernani, their leader, reveals his love for Elvira, lamenting that he will lose her forever to the aged grandee Don Ruy Gomez de Silva, who plans to marry her the next day. He asks his men to help him abduct Elvira, who has sworn to follow him.
Elvira's imminent marriage to Silva horrifies her, and she longs for Ernani to carry her away. Her companions show her an array of wedding gifts, but she can think only of Ernani.
Don Carlo, king of Spain, who also loves Elvira but knows she prefers Ernani, arrives at her apartment, eager to persuade her to forsake both the outlaw and the grandee. He asks Giovanna, her lady-in-waiting, to send Elvira to him. He ignores Elvira's icy reception, provoking her into threatening both their lives with a dagger. When Ernani appears, ready to abduct Elvira, she attempts to end the hostility between him and the king. Unexpectedly, Silva appears and is outraged to find the men with his betrothed Elvira. Without recognizing the intruders, he challenges them to a duel.
The king's chamberlain, Jago, announces Riccardo, the royal squire, who bows low to Carlo, thus revealing the king's identity. Silva is astonished and deeply embarrassed. Forgiving him, Carlo announces he will stay the night in Silva's castle, thereby entitling him to the old man's protection due to the laws of hospitality. Carlo then whispers to Ernani that he intends to save him, before declaring aloud that Ernani is a loyal subject and ordering his departure. To himself: Ernani reiterates his desire to avenge his father, as Elvira begs him to flee.
Guests have gathered in the hall of Silva's castle to celebrate his marriage to Elvira. Silva offers his hospitality to a pilgrim, who is actually the disguised Ernani. When Ernani learns that Elvira is to marry Silva, he throws off his disguise, offering as a wedding present his life and the reward the king has offered for it. Silva replies that his hospitality is sacred and protects all his guests, even from the king's anger. He orders his men to guard the castle's towers and sends Elvira to her apartment. Returning alone, Elvira explains to Ernani that after hearing reports of his death, she consented to marry Silva but planned to take her own life at the altar. As the reunited lovers embrace, Silva surprises them. Before the old man can vent his rage, the squire Jago enters to announce that the king has arrived at the gates. Silva gives orders for his welcome. The laws of honor and hospitality require him to protect Ernani as long as the bandit is under his roof. He orders his guest into hiding, then sends Elvira back to her apartment.
Don Carlo now enters and accuses Silva of rebellion, having noticed the armed men at the castle's towers. When Silva replies that he is a loyal subject, Carlo commands him to prove this by surrendering Ernani, who has been traced to the castle. Silva's sense of honor prevents him from complying. The king then issues an ultimatum: Ernani's head or Silva's. Silva offers his own and surrenders his sword to the king, who orders his men to search the castle for Ernani. Carlo threatens Silva with violent reprisals, but Silva refuses to betray his honor as a host. The king's men report that their search has failed. As the king is ordering torture to force tile secret from the castle's defenders, Elvira rushes in to beg the king for clemency. Carlo realizes he now has a new advantage: He demand Elvira—Silva's betrothed—as a hostage for the outlaw, and leads the unwilling girl away.
Ernani comes out of hiding and Silva challenges him to a duel, but the bandit refuses the uneven contest with an elderly opponent. He declares that he owes his life to Silva and asks to see Elvira once more before he dies. Upon learning that Elvira has been taken hostage, he persuades Silva to let him join the effort to rescue her. He makes a solemn vow to take his own life whenever Silva wishes, and gives the old man his hunting horn to sound at the moment he wishes to claim the forfeited life.
Knowing that his life is in danger and that his enemies are to gather at Charlemagne's tomb in Aix-la -Chapelle, Don Carlo arrives with Riccardo to spy on the conspirators. Elsewhere, the electors of the Holy Roman Empire are about to choose a new emperor. The king tells Riccardo to fire the tower's cannon three times if he has been selected. In that event, Riccardo is to bring Elvira to him. Alone, the king vows to emulate Charlemagne's virtues and prove himself worthy if he is elected emperor. He hides behind Charlemagne's tomb.
The conspirators gather and then draw lots to determine who will strike down the king. Silva draws the slip of paper bearing Ernani's name. The outlaw is elated at this chance to avenge his father, whom Carlo had robbed of his possessions and his life. Silva asks Ernani to yield the task to him, but Ernani refuses, despite offers to release the hold Silva has on his life. The embittered Silva renews his threat of vengeance.
Three cannon shots proclaim Carlo's election as emperor. He emerges from the chapel to defy the conspirators as a procession of electors arrives for his investiture.He decrees prison for the commoners among the conspirators and death for the noblemen. Ernani, whom the guards have placed among the commoners, steps forward to claim his place among the nobles, revealing that he is Don Juan of Aragon. Elvira, who had arrived in the procession of Electors, pleads for his clemency. Contemplating the tomb of Charlemagne, Carlo declares he will imitate the acts of his great predecessor. He pardons all the conspirators, then orders the marriage of Ern ani and Elvira.
Ernani's title has been restored to him, and guests are now enjoying the festivities following his wedding to Elvira. A masked stranger whose attire and attitude contrast sharply with the joyful wedding guests, now appears. Ernani, who has been rejoicing in his happiness with Elvira, is startled by the sound of a hunting horn. Increasingly unnerved, he sends the mystified Elvira to the bridal chamber to fetch some medicine, claiming that he is suffering from an old wound. Alone, Ernani wonders if he imagined the horn. Suddenly the masked guest reveals his identity: It is Silva, who has come toforce Ernani to keep his word. He offers Ernani the choice of poison or a dagger. Elvira returns and is horrified. The lovers' pleading is useless—Silva insists on the vengeance due him. Unable to break his vow, Ernani stabs himself.
Courtesy of Lyric Opera of Chicago