It is the 6th century BC. Nabucco (Nebuchadnezzar II), King of Babylon, has two daughters: Abigaille and Fenena. In truth, Abigaille was born to slave parents. Fenena, Nabucco's real daughter, is being held hostage in the Kingdom of Jerusalem, with whom Babylon is at war. Nabucco is poised to enter Jerusalem, and the Jews are in despair. The high priest Zaccaria brings Fenena before them, and reassures the populace that they have nothing to fear as long as they hold in their custody the daughter of the enemy king. It turns out Ishmaele, the nephew of the king of Jerusalem, is in love with Fenena. Abigaille storms into the Temple of Jerusalem with a band of Babylonian soldiers. Abigaille is in love with Ishmaele. She tells him that if he returns her love, she will help his people; Ishmaele says he cannot. Nabucco enters the temple and blasphemes against God. The outraged Zaccaria threatens to kill Fenena with a dagger, but Ishmaele takes the weapon from him. Nabucco orders the temple be burned, and takes the Jews as captives back to Babylon. High off his victory, Nabucco declares he is no longer king, but God. He is promptly struck by a thunderbolt and rendered senseless. Meanwhile, Abigaille has discovered a document showing that she is the child of slaves. She seethes with hatred for the lovers, Ishmaele and Fenena. Abigaille tricks the confused Nabucco and gets him to seal a death decree for the Jews and Fenena, who has converted to the Jewish religion out of love for Ishamaele. Abigaille destroys the document with the evidence of her true origins. She places Nabucco in confinement, and makes plans to seize the throne. The Jews, held prisoner on the banks of the Euphrates river, sing with longing for their homeland: "Va, pensiero, sull'ali dorate / Fly, thought, on wings of gold." Just as they and Fenena are about to be killed, Nabucco regains his senses. He begs forgiveness from Jehovah, and sets out to rescue Fenena. On his order, the Idol of Baal is destroyed, and the Jews are set free.