ACT I
Florestan, a political prisoner, is incarcerated in Seville. Disguised as a boy named Fidelio, Florestan's wife Leonore gets herself employed by the jailor, Rocco, whose daughter Marzelline then falls in love with the newcomer - to the anger of her lover Jacquino.
Fidelio begs to be allowed to work in the cells. Rocco agrees, but he must first ask the governor, Pizarro. Rocco cautions her that there is one cell which she can never enter.
Pizarro arrives and is given a letter in which he is warned that the minister, Don Fernando, intends to visit the prison, as he has heard rumours of cruelty there. Alarmed that he might be caught out, Pizarro tells Rocco that he is going to kill Florestan and demands that the jailor
prepare a grave.
Fidelio manages to persuade Rocco to allow the prisoners into the light, but Florestan is not among them. Furious that the prisoners have been let out, Pizarro orders them back into their cells.
ACT II
Florestan, starved and chained to a wall in his cell, begins to suffer hallucinations. He has a vision of an angel with Leonore's face, leading him from his life of suffering. Rising to follow her, he falls to the ground unconscious.
Rocco and Fidelio enter Florestan's cell, and even though his face is hidden, Fidelio swears to help the prisoner, no matter who he is. Florestan is woken and he and Leonore recognize each other.
When Pizarro enters, Leonore draws a pistol, holding the governor at bay while Don Fernando can be heard arriving.
Pizarro is arrested, the prisoners are released, and DonFernando addresses the people. Justice and love have triumphed over tyranny and hatred.
The opera ends in praise of the woman who risked her life to save her husband.