Part 1: The outlaw
Spain, 1519

Ernani was once a nobleman, but now leads a band of outlaws in the mountains of Aragon.  

He tells the men of his great love for the beautiful Elvira, and his plan to save her from an impending marriage to her uncle and guardian, Don Ruy Gómez de Silva. 

While Elvira waits for her lover, Don Carlo, King of Spain arrives to see her. He tells her he loves her, but tries to abduct her by force. Elvira resists and Ernani enters. 

The King recognises and taunts Ernani, and the two men prepare to duel, but Silva arrives. 

He is outraged to discover two men in his fiancée’s chamber and challenges them both. 

Carlo’s squire arrives and Silva realises he has threatened the King. He asks for forgiveness, and Carlo grants it, as he needs Silva’s support in the upcoming imperial election. 

Part 2: The guest 

Wedding preparations are underway at Silva’s castle. Ernani arrives in disguise, and Silva offers the pilgrim hospitality.  

When he discovers his guest with Elvira, he is angry and plans his vengeance. However, when the King arrives seeking his enemy Ernani, Silva is bound by his vow of hospitality to conceal him. Silva offers his own life as forfeit. When Elvira begs for mercy, the King takes Elvira hostage. 

Silva challenges Ernani to a duel, but is distracted when he discovers Carlo desires Elvira in marriage. 

Silva and Ernani agree to conspire against the King, and Ernani offers Silva his life in gratitude. He hands the old man a hunting horn, and says when he hears it sound, he will take his own life.