Scene I The throne room in the Pharaoh’s Palace in Memphis. The High Priest Ramfis informs Radames that Ethiopian army threatens Egypt.  The priests pray the goddess Isis to reveal the name of the commander who should lead the Egyptian army against the enemy. The High Priest Ramfis tells the Pharaoh the Goddess decision that Radames should be a commander. Radames is in love with Aida, the slave-girl of the Pharaoh’s daughter Amneris, who loves Radames and is jealous of Aida.  Amneris asks the slave-girl whether she loves Radames. The Pharaoh appears with the courtiers.  A messenger confirms that the Ethiopians are invading the Egyptian land.  Pharaoh tells Radames that he has to execute Isis will and lead the Egyptian army.  The crowd wishes the young leader a glorious victory over the Ethiopians, whose army is under command of their King Amonasro. Nobody in the hall suspects that Aida is Amonasro’s daughter…  She is alone and suffers from her conflict of loyalties – for whose victory should she pray: for her beloved Radames or for her father King Amonasro? Scene II A temple in Memphis. Priests, praying to the Gods for a victory, are consecrating Radames’ sword in a sacred ritual.  The High Priest Ramfis gives the commander the blessed weapon.

Scene I The chamber of Amneris. Ethiopia has been defeated.  Amneris, entertained by slaves, prepares for Radames triumphal return.  She wants to know what Aida is thinking about.  Therefore, when Aida appears, Amneris first claims that Radames is dead, and then says that he is still alive.  Aida reacts with horror that is followed by joy.  This proves to Amneris that the slave loves the commander. The jealous and vindictive Amneris threatens the slave with death if only she reveals her feelings to Radames.  To humiliate the girl, the Princess orders her to serve at the banquet given in honour of Radames’ victorious campaign. Scene II The square in Thebes. The crowd joyfully welcomes Radames who is in command of his victorious army.  The Pharaoh, Amneris, priests and courtiers arrive to observe the festivity.  Servants and slaves, with Aida among them, come after them. The Pharaoh thanks Radames for the triumphant victory and promises to fulfill all his wishes as a reward.  Radames wants to see the Ethiopian captives before saying his wish. Aida notices her father King Amonasro among the captives.  She cannot control herself and falls on his neck.  The King of Ethiopia is pretending to be a common warrior and gives Aida a sign to keep his real identity in secret.  Amonasro tells the Pharaoh that the King of Ethiopia died in the battle. The captives appeal for pardon but the High Priest Ramfis assures the Pharaoh that the Gods wish the captives’ death.  The people of Egypt are about to pardon the prisoners and ask the priests for mercy.  Radames implore for forgiveness too.  The Pharaoh decides to keep his promise to Radames and frees the captives.  The High Priest advises the Pharaoh to keep Aida and her father as hostages – peace must be maintained on the Egyptian borders.  The Pharaoh agrees with the priests and also announces about the betrothal of his daughter and Radames.

Isis temple on the bank of the Nile. Amneris and Ramfis enter the temple to pray for a happy marriage. Aida appears nearby.  She has come to meet Radames and while waiting for him she feels nostalgia for her homeland.  Amonasro appears and orders his daughter to ask Radames about the place of the future attack on Ethiopia.  At first Aida refuses with horror.  Amonasro is about to curse his daughter, who has forgotten the despair of her people.  Aida is not able to endure her father’s curse and agrees. Radames appears.  He reveals his love to Aida and assures her that he needs neither the Pharaoh’s honours, nor the throne of Egypt.  If he comes back victorious from Ethiopia, he will tell the Pharaoh about his secret love to the slave-girl.  Aida doesn’t believe him.  She knows how cruel Amneris’ revenge can be.  There is only one solution for them – to flee from Egypt to Ethiopia, which will become a new homeland to Radames. Radames doesn’t want to betray his country.  His heart is torn between his love to Aida and devotion to his motherland.  Love wins… Aida asks Radames which road is still not occupied by the Egyptian army.  Radames betrays military secret. Suddenly Amonasro steps out from his hiding place.  He tells Radames his real name and offers him the throne and safety in Ethiopia. Those last words are overheard by Amneris and the High Priest Ramfis.  He orders the guards to arrest the traitor. Amonasro snatches up a knife and tries to kill Amneris, but Radames steps between them.  Amonasro and Aida run away.  Radames surrenders and gives his sword to Ramfis.

Scene I Amneris orders to bring Radames to her from the prison.  She offers to save him if he renounces Aida and marries her.  Radames refuses – it is better to die than to live without Aida. Finding out from Amneris that Amonasro died during his escape but his daughter is still alive, Radames is firmly convinced in his decision.  Amneris asks him to forget Aida and save his life, but Radames remains firm. The guards take the prisoner back to jail.  Priests gather for the judgement.  The sentence is harsh – as a traitor Radames will be buried alive in a crypt beneath the temple.  Amneris hears the sentence.  She reveals her love to Radames and curses the judges. Scene II Beneath the temple where Radames will be buried. Sounds of funeral prayers are heard from the temple.  Radames is awaiting his death. His last thoughts are about Aida.  He hopes she is free and happy in her homeland.  But Aida is nearby.  She has heard the judges’ sentence and has entered the crypt earlier to share her beloved’s fate.  Amneris faints and falls on the stone which blocks the entrance to the tomb.  Aida and Radames bid farewell to earth and greet eternity as Amneris prays to Isis for peace.