Marzelline, Rocco’s daughter, struggles with Jaquino, her former boyfriend and a prison em­ployee, who still loves her. She has fallen in love with “Fidelio”, whose meticulous work has gained Rocco’s admiration, and Rocco pushes for their engagement, setting a wedding date after Pizarro’s imminent visit. Rocco, considering their bleak surroundings, says that it will take more than love to make a go of it-money must be made. Leonore asks if she might help Rocco with the secret prisoners, and he agrees to ask Pizarro’s permission, as this work is taking a toll on him. Talk turns to one particular prisoner, who Rocco says has been there two years and is near death. Leonore senses that this might be Florestan.

Pizarro arrives, orders soldiers to watch the road, and reads his dispatches. Among them is a letter alerting him to the imminent arrival of his com­manding officer, Fernando, and urging him to dispose of prisoners who pose a threat to his safety. Pizarro orders Rocco to dig a grave in one particular cell, where he himself will murder the prisoner. Leonore summons courage and hope to face off her enemy and reach her husband, then learns from Rocco that Pizarro will allow her to help Rocco with the secret prisoner. She encour­ages Rocco to let the prisoners into the courtyard for some air. Rocco complies, incurring the stunned gratitude of the prisoners but also Pizarro’s rage.

Florestan, chained in a dungeon, struggles with his fate and imagines Leonore appearing to save him or to take him to heaven. Rocco and Leonore enter and begin to dig Florestan’s grave, and Leonore soon recognizes her husband. Rocco, touched by Florestan’s physical and emotional condition, and by his grim fate, warily allows him a sip of wine before Pizarro arrives, knife in hand. As Pizarro attacks Florestan, Leonore steps be­tween them, pointing a gun at Pizarro and reveal­ing her true identity. Trumpets announce the arrival of Pizarro’s commander and troops, Jaquino brings help, and Pizarro is led away. Leonore and Florestan embrace.

Fernando has liberated the prison. The prisoners celebrate: “Justice and mercy have appeared at the edge of our grave.” Fernando also greets Florestan, whom he thought dead, and learns the truth. Pizarro is taken away, and Fernando asks Leonore to unlock Florestan’s chains, a tribute to her heroism, which is hailed by the crowd.