ACT 1

Egypt is being threatened by the Ethiopians. Ramfis, the High Priest, tells Radames that the goddess Isis has already nominated the captain who is to lead the Egyptian army in battle. The young warrior, who hopes that he is the chosen one, gives voice to his dreams of glory and to his love for Aida, a young Ethiopian slave. But Amneris, Pharaoh's daughter, is also secretly in love with Radames, and the young man's evasive answers to her questions lead her to suspect the existence of a rival; her doubts are turned to certainty when she observes Aida's behaviour. Pharaoh and his court make their entrance, and a messenger brings news that the Ethiopian enemies, led by their king Amonasro, are marching on Thebes. The High Priest now reveals that it is Radames who has been chosen by Isis: the fate of Egypt is now in his hands. Radames is overjoyed and amidst the general acclamation goes to the temple of Vulcan to be consecrated. Aida, who has joined the others in auguring him a victorious return, remains alone, overwhelmed by her conflicting passions: unknown to the Egyptian court, she is the daughter of the Ethiopian king, and now her father and the man she loves will face each other as enemies on the battlefield at the head of two warring armies.

In the temple of Vulcan, priests and priestesses invoke the god Phta, creator of the world. Radames dons the consecrated armour whilst accompanied by ritual dances and hymns, Ramfis invokes the protection of the gods.

ACT 2

The invading Ethiopians have been routed for the while and Amneris is preparing to celebrate the return of the hero, Radames. The Princess pretends compassion for Aida, who is grieving over the defeat suffered by her people; Amneris slyly suggests that perhaps Aida's grief and anguish have been heightened by her love for one of the warriors ; but fate will surely be less cruel to her beloved than to Radames, who has fallen in battle. At this news Aida can no longer conceal her distress and mourns the loss of her lover. Amneris now reveals the trap she has laid: Radames is alive and is returning in triumph. The young slave girl confesses her love and begs for pardon but Amneris, now certain of what she had formerly only guessed, threatens her with vengeance.

Pharaoh, accompanied by his ministers, his court and the High Priest, takes his place at one of the great gates of Thebes to preside over the victory celebrations. Greeted by the acclamations of the people, the great procession passes and at last Radames appears; Amneris crowns him with a laurel wreath. Radames intercedes for the prisoners, amongst whom is Amonasro who, recognising his daughter Aida, warns her not to reveal his identity . Despite the protests of the priests, Pharaoh promises to grant the Ethiopians their freedom but, following the advice of Ramfis, decides to keep Aida's father as a hostage. The king thereupon announces that as a sign of supreme favour he will grant Radames the hand of his daughter Amneris. The Princess rejoices, while Radames and Aida cannot conceal their despair. Amonasro tries to console Aida, assuring her that all is not lost, as it would seem, and that vengeance of their people is at hand.

ACT 3

Accompanied by the High Priest, Amneris withdraws to the temple of the goddess Isis to keep vigil before her forthcoming marriage. Nearby Aida is awaiting Radames. Amonasro appears stealthily and orders her to get Radames to reveal the route that the Egyptian army will take going out to do battle with the Ethiopians. Aida rebels at the idea of taking advantage of Radames' love for her, but in the end her love both for the father and for the country, for which she longs, gets the upper hand and she promises to obey. When Radames arrives Aida reproaches him for having yielded to Pharaoh's orders and agreed to the marriage with Amneris. She proposes that they flee together to Ethiopia and asks him what path the Egyptian army will be taking, so as to avoid them. The Gorge of Napata, is Radames' reply. Amonasro, who from his hiding place has heard everything, now cries out exultantly that it is in the Gorge of Napata that the Ethiopian army is waiting in ambush. Radames realises that he has been trapped into making this revelation and on learning that Aida's father is none other than the King of the Ethiopians he acknowledges his involuntary betrayal of his country. Amonasro urges him to flee, declaring that he now has no other choice. But it is too late, for Amneris, coming out of the temple, discovers them together. Amonasro tries to attack her but is prevented from doing so by Radames, who gives himself up to the High Priest as a prisoner.

ACT 4

Amneris, who is still in love with Radames and determined to make a last attempt to save him from death, manages to have the prisoner brought before her. She promises that she will intercede on his behalf if he swears to renounce Aida forever. But Radames is determined to expiate with his life the treason he has committed, and replies that he will not even attempt to defend himself when the judges interrogate him. The guards take the prisoner back to dungeons to be tried by the priests. Amneris hears in despair that he has been condemned to be buried alive. In vain she hurls curses at the judges who reappear after passing sentence.

Radames has already been walled up in a tomb beneath the temple of Vulcan; suddenly perceiving a figure in the shadows he realises that he is not alone. Foreseeing the tragic sentence, Aida has slipped into the tomb by stealth in order to die with him. Overcome with remorse at being the cause of the death of his beloved, Radames desperately tries to raise the stone that seals the tomb, but all in vain. Reconciled to their fate the lovers serenely await death. Above them, kneeling on the stone that  separates the temple and the tomb, Amneris prays.