Seville, mid-eighteenth century. After the Marquis of Calatrava bids good night to his daughter, Leonora di Vargas, she tells her maid, Curra, about her imminent elopement with her lover, Don Alvaro. Hesitant to leave her father, Leonora is nevertheless torn by her love for Alvaro, an Inca of royal descent. Climbing in via the balcony, Alvaro reassures her, then accuses her of not loving him. She agrees to leave, but her father, awakened by noise in the courtyard, storms in with sword drawn, challenging Alvaro, who throws his pistol to the floor. It goes off by accident, fatally wounding the Marquis, who dies cursing his daughter. The lovers flee.
An inn at Hornachuelos. Amid peasants and mule drivers, Don Carlo di Vargas, Leonora’s brother, posing as “Pereda,” a student from Salamanca, hunts for his sister and her lover to avenge the Marquis’ death. Leonora, disguised as a man, comes to the door and recognizes her brother. Separated from Alvaro during their flight, she is traveling with a muleteer, Trabuco, who endures jibes as to the identity and sex of the “little person” with him. Preziosilla, a Gypsy girl, offers to tell fortunes and inspire morale for the upcoming battles of Italy and Spain against the Germans. She tells Carlo he is no student, while Leonora wonders how she can escape from her vengeful brother. Pilgrims en route to Holy Week celebrations arrive, and everyone joins in prayer. At the urging of the Alcalde (local mayor), Carlo tells the gathering he is a student, mentioning his friend “Vargas,” who is bent on avenging the death of his father at the hands of his sister’s lover.
Outside the church and monastery of the Madonna degli Angeli, Leonora, still in male clothes, prays for the Virgin’s forgiveness. Evening prayers are heard from within. She sounds the monastery bell and is greeted gruffly by Brother Melitone, who tries to send her away till next morning. She says she has been sent by Father Cleto to see the Padre Guardiano (Father Superior). When he appears, she tells him she is Leonora di Vargas, about whom Father Cleto has written. She asks to become a hermit and live in a cave, devoting herself only to God. When he learns her brother is bent on killing her, the Padre Guardiano agrees.
Near a battlefield in Velletri, Italy, soldiers are gambling. Alvaro, now in the military, laments his outcast state, praying to Leonora — whom he believes dead — to pity him. Hearing the cries of another officer, he goes to the rescue and returns with Carlo. Neither man is aware of the other’s identity, and both are using assumed names. Carlo thanks Alvaro for saving his life from soldiers who were quarreling over cards. They swear friendship in life and death, then run off to battle.
The wounded Alvaro, borne in on a stretcher, asks Carlo to burn his private papers when he dies. Carlo agrees, but when his friend is removed for surgery, he muses on the possibility that Alvaro might be the “cursed Indian” who killed his father and dishonored his sister. Looking among Alvaro’s belongings, he finds a portrait of Leonora. As word comes that Alvaro’s life has been saved by surgery, Carlo exults that his enemy will live — to suffer his personal revenge.
Some time later, Alvaro encounters Carlo, who announces he has found out who he is and wants to fight. Alvaro tries to pacify him, saying that Leonora, if still alive, as Carlo says, should be the object of their joint search. Carlo bullies him into a rage, and they fight, but a patrol separates them. Alvaro, repenting of his anger, resolves to enter a monastery. As the sun rises, soldiers and civilians crowd the scene, led by Preziosilla, telling fortunes, and Trabuco, peddling cheap merchandise. Melitone stumbles upon the motley gathering of people and lectures them on their ungodly ways. Finally, Preziosilla, wearing a drum around her neck, leads an unaccompanied marching chorus in imitation of a military drummer’s sound.
Five years later. Inside the monastery, back on Spanish soil, beggars wait for Melitone to dole out soup while the Padre Guardiano cautions him against being impatient with the poor, who are dear to God. The gate bell rings, announcing Carlo, who demands to see “Father Rafaello,” Alvaro’s assumed name. As he waits, he vows to kill his enemy. Alvaro pleads for peace between them, but again Carlo goads him, and they rush off to find a dueling place.
Leonora emerges from her cave, disheveled and distressed, to pray for the peace that continues to elude her: in her heart she still loves Alvaro. Hearing a commotion nearby, she retreats into the cave, only to be summoned forth by Alvaro himself: having mortally wounded Carlo, he asks the hermit to give absolution to the dying man. They recognize each other, and Alvaro cries that once again he has the blood of her family on his hands. Leonora goes to Carlo, who with his last strength deals her a mortal blow. The Padre Guardiano enters and silences Alvaro’s frustrated rage as Leonora gasps that she will await him in heaven.