ACT I 
Egypt, during the reign of the pharaohs. At the royal palace in Memphis, the high priest Ramfis tells the warrior Radamès that Ethiopia is preparing another attack against Egypt. Radamès hopes to command his army. He is in love with Aida, the Ethiopian slave of Princess Amneris, the king’s daughter. Radamès dreams that victory in the war would enable him to free her and marry her (“Celeste Aida”). But Amneris loves Radamès, and when the three meet, she jealously senses his feelings for Aida. A messenger tells the King of Egypt and the assembled priests and soldiers that the Ethiopians are advancing. The king names Radamès to lead the army, and all join in a patriotic anthem. Left alone, Aida is torn between her love for Radamès and loyalty to her native country, where her father, Amonasro, is king (“Ritorna vincitor”). She prays to the gods for mercy.

In the temple of Vulcan, the priests consecrate Radamès. Ramfis orders him to protect the homeland.

ACT II 
Ethiopia has been defeated, and Amneris waits for the triumphant return of Radamès. When Aida approaches, the princess sends away her other attendants so that she can learn her slave’s private feelings (Duet: “Fu la sorte dell’armi”). She first pretends that Radamès has fallen in battle, then says he is still alive. Aida’s reactions leave no doubt that she loves Radamès. Amneris, determined to be victorious over her rival, leaves for the triumphal procession.

At the city gates, the king and Amneris observe the victory celebrations and praise Radamès’s triumph. Soldiers lead in the captured Ethiopians, among them Amonasro, who signals his daughter not to reveal his identity as king. Amonasro’s eloquent plea for mercy impresses Radamès, and the warrior asks that the order for the prisoners to be executed be overruled and that they be freed instead. The king grants his request but keeps Amonasro in custody. He declares that as a victor’s reward, Radamès will have Amneris’s hand in marriage.

INTERMISSION

ACT III 
On the eve of Amneris’s wedding, Ramfis and Amneris pray in a temple on the banks of the Nile. Nearby, Aida is waiting for Radamès, lost in thoughts of her homeland. Suddenly, Amonasro appears. Appealing to Aida’s sense of duty, he makes her promise to discover from Radamès which route the Egyptian army will take to invade Ethiopia. Amonasro hides as Radamès arrives. He and Aida dream about their future life together, and Aida convinces him to run away with her. Aida asks him about his army’s route, and just as he reveals the secret, Amonasro emerges from his hiding place. Realizing what he has done, Radamès is horrified. Aida and Amonasro try to calm him when Ramfis and Amneris emerge from the temple. Father and daughter are able to escape, but Radamès surrenders himself to the high priest’s guards.

ACT IV 
Radamès awaits trial as a traitor, believing Aida to be dead. Amneris summons him, but even after he learns that Aida has survived, he rejects Amneris’s offer to save him if he gives up his lover. Brought before the priests, Radamès refuses to answer their accusations, and they condem him to be buried alive. Amneris begs for mercy, but the judges will not change their verdict.

Aida has hidden in the vault to share Radamès’s fate. They express their love for the last time while Amneris, in the temple above, prays for peace.