ACT I
Jerusalem, 6th century B.C. The Israelites are praying for help against Nabucco, King of Babylon, who has attacked them. Zaccaria, their high priest, reassures his people that the Lord will not forsake them. As the Israelites leave, Ismaele, nephew of the King of Jerusalem, is left alone with Nabucco’s daughter Fenena, whom the Hebrews hold hostage. The two fell in love during Ismaele’s imprisonment in Babylon, and Fenena helped him escape and followed him to Jerusalem. They are interrupted by the sudden appearance of Fenena’s half-sister, Abigaille, and a band of disguised Babylonian soldiers. Abigaille, who is also in love with Ismaele, tells him that she can save his people if he will return her love, but he refuses. The Israelites rush back into the temple in a panic. When Nabucco enters with his warriors, Zaccaria confronts him, threatening to kill Fenena. Ismaele disarms the priest and delivers Fenena to her father. Nabucco orders the destruction of the temple.


ACT II
Nabucco has appointed Fenena regent while he is away leading his campaign. Abigaille, in the royal palace in Babylon, has found a document saying that she is not the king’s daughter but the child of slaves. She swears vengeance on Nabucco and Fenena. The High Priest of Baal arrives with news that Fenena has betrayed them and freed the Israelite prisoners. He offers the throne to Abigaille and proposes to spread the rumor that Nabucco has fallen in battle.

Zaccaria hopes to persuade the Babylonians to give up their false idols. The Levites accuse Ismaele of treachery, but Zaccaria announces that he has been pardoned for saving a fellow Israelite—the newly converted Fenena. A messenger warns Fenena that the king is dead and her life is in danger. Before she can escape, the High Priest of Baal arrives with Abigaille and the Babylonians, who proclaim Abigaille ruler. She is about to crown herself when, to the astonishment of all, Nabucco appears. He takes the crown from her and declares himself not only king but god. At this, a thunderbolt strikes him down. Abigaille, triumphant, retrieves the crown for herself.


INTERMISSION


ACT III 
The Babylonians hail Abigaille as their ruler. The High Priest urges her to have the Israelites killed, but before she can give the order, Nabucco appears in a state of half-madness. Abigaille tricks him into signing the death warrant for the captive Israelites. Fenena, she says, must also die. When Nabucco starts to look for the document proving Abigaille’s ancestry, she produces it and tears it to pieces. He pleads in vain for Fenena’s life.

On the banks of the Euphrates, the Israelites remember their lost homeland. Zaccaria tells them they will overcome captivity and obliterate Babylon with the help of God.


ACT IV 
Nabucco, locked up in his apartments by Abigaille, watches Fenena and the Israelites being led to execution. He prays to the god of Israel for forgiveness, pledging to convert himself and his people. His sanity restored, he forces open the door and summons his soldiers to regain the throne and save his daughter.

The Israelites are about to be executed. Fenena prays to be received into heaven when Nabucco rushes in and stops the sacrifice. Abigaille, full of remorse, takes poison and dies, confessing her crimes and praying to the god of Israel to pardon her. Nabucco announces his conversion and frees the Israelites, telling them to return to their native land and rebuild their temple. Israelites and Babylonians are united in praising God.