Act 1
In ancient Egypt, at the royal palace at Memphis, Ramfis, the high priest, informs young army captain Radames that Ethiopian forces are again challenging Egypt’s power in the Nile Valley. Radames hopes he will be chosen to command the army, as a victory would allow him to free his secret love, Aida, the Ethiopian slave of Egyptian Princess Amneris.

Amneris, who loves Radames, arrives and senses his feelings for Aida. She is jealous. The King arrives with a procession and confirms that the Ethiopians, under the command of their ruler, Amonasro, are advancing on the sacred city of Thebes. The King announces that the goddess Isis has named Radames to lead the Egyptian retaliation. War cries fill the air as the Egyptians leave to prepare the attack.

Left alone, Aida is torn between her love for Radames and for her homeland: though now a slave, she is in fact the daughter of Ethiopian ruler Amonasro. She prays for mercy. In the temple, as the priestesses dance and chant the praises of the god Phtah, the priests ritually consecrate Radames’ sword.

Act 2
Ethiopia has been defeated. Amneris, entertained and groomed by slaves, prepares for Radames’ triumphant entry into Thebes. When Aida approaches, Amneris tries to discern her slave’s private feelings, first by pretending that Radames is dead, then confirming he is alive. Aida’s response – grief, then elation – makes it clear that she loves him. Amneris leaves for the festivities after warning Aida to remember her place as a slave and quash her feelings for Radames.

At the city gates, a parade and dance celebrate the Egyptian victory. Amneris crowns Radames with a victor’s wreath. His captives are lead in; among them is Amonasro, disguised as an officer. He warns Aida to not give away his kingly identity. Amonasro makes an eloquent plea for mercy, and Radames, impressed, asks that the priests’ decree of death to the prisoners be overruled. The king grants this and gives him the hand of Amneris in marriage, but at Ramfis’s urging orders that Amonasro be kept prisoner.

Act 3
Ramfis leads Amneris to a temple of Isis on the banks of the Nile for a wedding vigil. Aida, waiting nearby for Radames, is overcome with nostalgia for her conquered homeland. Amonasro suddenly appears. Preying on her feelings, he entreats Aida to betray Radames by eliciting from him the route his army will take into Ethiopia. Aida agrees to obey her father’s wishes. Radames arrives, ardent with dreams of their future life together. Just as he reveals the military secret, Amonasro appears from hiding. Radames is horrified by his unwitting act of treason. Ramfis and Amneris come forth from the temple. While Aida escapes with her father, Radames surrenders to the priests as a traitor.

Act 4
In the temple of judgement, Radames refuses Amneris’s offer to save him if only he will renounce Aida and marry her instead. When he is led away, her pride dissolves and she declares that in her jealous fury she has condemned Radames to death and herself to unending woe. Amneris listens as three times the priests ask Radames to defend himself. When he refuses to answer he is sentenced to death. As they slowly move off, Amneris begs for mercy and curses the priests’ lust for revenge.
Buried alive in a tomb below the Temple of Vulcan, Radames is joined by Aida, who has hidden there to share his fate. The lovers bid farewell to earth, while above, the sobbing Amneris prays to Isis and implores peace. The priests invoke Phtah as the curtain falls.