ACT I
Marzelline, daughter of the prison warden Rocco, rejects the attentions of her father’s assistant, Jaquino, who wants to marry her. She has fallen in love with his hardworking new assistant, Fidelio. Rocco approves of the match and tells her that he will seek permission for the marriage from Don Pizarro, the governor of the prison. But Fidelio is in fact Leonore. Desperately searching for her husband, Florestan, who has been held as a political prisoner for two years, she has disguised herself as a man. When Rocco mentions a prisoner lying near death in a subterranean cell, Leonore suspects it might be Florestan and begs Rocco to take her on his rounds, even though it is forbidden.

Pizarro learns that Don Fernando, minister of state, is on his way to inspect the prison. He realizes that if Fernando discovers that his friend Florestan is alive, all Pizarro’s plans will be lost. He tries to bribe Rocco to murder Florestan, but Rocco refuses. He then decides to kill him himself and orders Rocco to dig the grave. Leonore, who has overheard Pizarro, prays for the strength to save her husband. She asks for the prisoners to be given a few moments of fresh air, which Rocco grudgingly allows. Pizarro orders them back into their cells and makes it clear to Rocco that he must not disobey orders. Rocco and Leonore descend into the prison to dig the grave.

INTERMISSION

ACT II
In his cell, Florestan hallucinates that Leonore has arrived to free him. But his vision turns to despair, and he collapses in exhaustion. Rocco and Leonore appear and begin digging the grave. Florestan awakens, not recognizing his wife, and Leonore almost loses her composure at the sound of his voice. Florestan asks for water. Rocco offers him wine and allows Leonore to give him some bread. When everything is ready, Pizarro appears. As he is about to kill Florestan, Leonore reveals her identity and stops Pizarro with a gun. A trumpet is heard—Don Fernando has arrived. Rocco and Pizarro leave to meet him as Leonore and Florestan are reunited.

In the prison courtyard, Don Fernando proclaims justice for all. He is amazed when Rocco brings his old friend Florestan before him and relates the details of Leonore’s heroism. Pizarro is arrested, and Leonore frees Florestan from his bonds. The other prisoners are freed as well, and the people hail Leonore.