ACT I,Scene 1

Marzelline, daughter of the jailer Rocco, has fallen in love with 'Fidelio' (really Leonore), who has been working at the prison for six months or so, but whose origins are unknown. Marzelline believes that Fidelio returns her love and wishes to marry him; she therefore gratefully turns down Jaquino the gatekeeper in a confrontation with him.

When Rocco comes upon them, Jaquino asks for Marzelline's hand in marriage, but Rocco rejects him. He warns the young people to be sure about whom they marry, since a mistake is not reversible. Marzelline reiterates her wish to marry Fidelio and Jaquino has to admit that he has no chance.

Fidelio comes back from shopping, carrying chains and food. Rocco praises the young man because he always manages to get cheaper prices than he, Rocco, can. The jailer believes Fidelio is so eager to please because he loves Marzelline and fixes an early date for the wedding in Marzelline's presence. At the same time he lectures the young people about the value of money, warning them that a household cannot be built on love alone.

Leonore, however, is pursuing a quite different aim by dressing up as a young man. She is looking for her lost husband whom she believes is in the prison. For this reason, and not for the first time, she offers Rocco her help in the dungeons. Rocco finally agrees to ask Pizarro, the prison director, for permission. He points out however that he cannot allow Fidelio access to one particular prisoner who has been languishing there for two years. It appears that the prisoner has powerful enemies and Pizarro wants to let him starve to death.

Act II

Pizarro is informed by one of his spies that the minister is to inspect the prison unannounced the next day, because he has heard that Pizarro is wrongly holding some prisoners there. The governor had Florestan, Leonore's husband, thrown in prison for threatening to reveal details of Pizarro's misdeeds and he now fears he will be detected. When Rocco refuses to kill the prisoner, Pizarro decides to do it himself. He tells Rocco to dig a grave in the prison. Pizarro strengthens the guard and has the tower guarded.

Leonore is troubled that she must deceive Marzelline. They talk about marriage and decide that loyalty is most important. A woman should obey her husband and have no secrets from him. Playing her role, Leonore says she suffers from not knowing her father and Marzelline tries to drive away the dejected thoughts of Fidelio.

Leonore takes courage. She is certain that her husband is in the prison and it is the duty of a loyal wife to save her husband.

In Scene 4 the prisoners take new hope from their daily exercises. Rocco tells Fidelio that the governor has agreed to the marriage and to Fidelio helping Rocco. First they have to dig a grave for the prisoner whom Pizarro intends to kill that very day. Leonore has to pull herself together in order not to lose countenance. Marzelline comes running up and warns her father of Pizarro, who is hot on her heels and angry with Rocco. Pizarro comes in with soldiers and goads Rocco into working faster.

Act III

Florestan is enduring his fate in the knowledge that he has told the truth. He thinks of his wife and prays that she may find peace in the thought that he was right. Exhausted, he lies down. Rocco and Leonore begin to dig the grave. Rocco urges haste. At first Leonore does not recognize her husband. When Florestan comes round, Rocco wishes to speak with him and Fidelio is supposed to continue digging. Florestan asks the jailer, as he has often done before, who the governor of the prison is and this time Rocco tells him. Florestan now knows why he must suffer so and asks Rocco to send a message to his wife Leonore in Seville, because she can help him. Rocco refuses - saying that it is too dangerous and probably of no use. Florestan asks at least for a little water. Leonore, who has been listening to this conversation, brings him some wine and gives him a piece of bread. Rocco calls Pizarro.

Taking his dagger, Pizarro reveals himself to Florestan. Before Pizarro can stab the prisoner, Leonore comes between them, identifying herself as Florestan's wife and drawing a pistol. At the same moment the arrival of the minister is announced. Rocco takes the weapon from Leonore and follows the fleeing Pizarro.

Leonore loses all hope after the pistol is taken from her, but the young couple are overjoyed to hold each other in their arms again. Leonore tells Florestan how she reached him and refuses his gratitude. Outside we hear cries of revenge. The two lovers assume this refers to them and decide to die together.

The minister appears, led by Rocco. He calms the young couple; he has come to free them and to revenge the misdeed. Rocco renounces his connections with Pizarro and Fernando swears to bring Pizarro to justice before the king. Leonore's courage is praised by all. Loyalty, virtue and true love have triumphed.