The high priest Ramfis tells the young warrior Radames that Egypt is threatened by war with the Ethiopians and that the goddess Isis has named the man who will lead the armies of Egypt against the invaders. Left alone, Radames expresses his hopes that he will be the one chosen and reflects on his secret love for the Ethiopian slave Aida. He is approached by the princess Amneris, who loves him and suspects she has a rival. Aida enters and admits her foreboding of war. She attempts to conceal her grief for her own country as her Egyptian captors do not know that she is the daughter of Amonasro, King of Ethiopia. Amneris becomes suspicious of Aida and Radames.
The king is told of the border attacks by the Ethiopians led by Amonasro and that Radames has been chosen to lead Egypt 's armies. Aida reflects in horror at having joined in the call to battle, conflicted by loyalty to both her lover and her own father and people.
Ramfis chants an invocation to the god Phta with other priests and priestesses. Radames approaches the alter. The High Priest asks the aid of the gods in protecting Egypt . Radames repeats the prayer, and chorus breaks out into a great cry to the almighty Phta.
Amneris is preparing for Radames's return. Aida enters and Amneris feigns sympathy for the slave as her people were defeated. She tricks Aida into admitting her secret love by pretending that Radames has been killed in the war. When the truth is revealed, Amneris confronts her adversary.
The victorious Egyptian army returns to great adulation as the people sing a hymn to the gods. The Ethiopian prisoners are brought in, and among them Aida recognizes her father Amonasro. He tells her not to reveal his true royal identity, as he is posing as a common soldier. Radames asks the king to be merciful toward the prisoners, but Ramfis and the priests insist that, if released, the Ethiopians will again pose a threat. Finally, it is agreed Amonasro, at least, will be kept as a hostage. To reward Radames for his efforts, the king offers the hand of his daughter Amneris.
On the eve of her wedding day, Amneris prays at the temple of Isis with Ramfis. Nearby, Aida appears for a rendezvous with Radames. She vows to throw herself in the Nile if he should fail to appear and sings of her homeland. Amonasro steps out of the shadows, telling her she can both defeat her rival and see her country again if she can get Radames to reveal which road the Egyptian troops plan to take in their next campaign. Aida is hesitant, but Amonasro accuses her of being disloyal and describes the inevitable destruction of Ethiopia if she fails to cooperate. He hides as Radames appears. With marriage to Amneris imminent, Aida questions his devotion, but Radames tells her that war has erupted again, and after he has once again led Egypt to victory, he will be able to ask for Aida's hand as a reward. She suggests instead they flee together to her native land, but when Radames recoils at the suggestion, she accuses him of not loving her. He finally agrees to her plan. Remembering her oath to her father, Aida asks Radames what road would be the safest to take to avoid running into the Egyptian army, and he divulges that the troops will pass through the Napata gorge. Amonasro jumps out from his hiding place, and Radames realizes what he has done. Having heard his treachery, Amneris emerges from the temple, and Ramfis takes an unresisting Radames into custody as Amonasro and Aida make their escape.
Amneris paces nervously as Radames faces judgment. She urges him to defend himself, saying she will use her influence to save his life, but he refuses. The charges are read and Radames says nothing in his own defense. He is found guilty and is condemned to be entombed alive below the altar of the god he has offended.
Once inside the tomb, Radames senses he is not alone and soon finds Aida. The two doomed lovers bid farewell to earth as Amneris, kneeling above the tomb, prays for peace.
Courtesy of Minnesota Opera