The conflict between romantic love and love of family and country.
Scene 1 The gods have selected the person to lead Egypt into battle with Ethiopia. After a conversation with Ramfis, High Priest, Radames alone speaks of hope accompanied by fanfares of battle that he will be that person. He turns his attention to his "heavenly Aida." After the entrance of Amneris, Aida makes her first appearance--the love triangle is onstage together for the first time. Amneris is jealous and Aida is torn between love of Radames and love of country. After the entrance of the king and confirmation of the selection of Radames, Aida alone considers what will happen to her father, her homeland and her brothers as the one she loves goes to war against them. The aria continues and the scene ends with a prayer to her gods.
Scene 2 The priests gather before Radames is brought into the temple for the solemn rites before he enters into battle for Egypt. The scene includes sacred dance and great atmospheric music .
The battle is over, and Amneris prepares for the triumphant return of the soldiers. The jealous princess tries to discover Aida's true feelings by pretending that Radames died in battle. Amneris judges Aida's reaction, and the scene ends with Aida praying to her gods (same melody as end of Act I, Scene 1.).
This grand scene is the centerpiece of the opera, and about as grand as opera gets. It is a celebration and processional with dance, with on-stage music, and a dramatic surprise. The king grants the victor, Radames any wish. He wishes for freedom for the Ethiopian prisoners (the people support his wish, the priests do not). The Egyptian king grants another reward: "Let Amneris's hand be your reward." When the prisoners enter, one is revealed to be Aida's father, but his identity as Amonasro, King of Ethiopia is hidden until the end of Act III. The prisoners are freed and they return to Ethiopia, with the exception of Aida and her father. The great scene ends with Amonasro thinking revenge, Amneris hopeful of marriage, Aida with tears of a desperate love, and Radames: "The throne of Egypt is not worth [breaking] Aida's heart."
In this act Aida has a solo aria and two great duets. The night before the proposed wedding, Amneris goes to the Temple of Isis to pray. Aida sings of her beloved country: "never shall I see [my homeland] again...now that the dream of love has vanished." In a duet with her father, Amonasro pressures her into getting Radames to reveal the secret road that the Egyptians will use before another battle with Ethiopia. In Aida's second duet, a duet with Radames, he reveals the secret road. Amonasro reveals his identify as King of Ethiopia, Amneris witnesses the betrayal by Radames, and Radames surrenders to the priests.
This is the judgement scene where Radames appears before the priests. Amneris will save him if he renounces Aida. He will not, and he is sentenced to death.
A two-part stage (the Temple of Vulcan and a vault below) is the scene for the final moments of the opera. All three--the love triangle--are in view of the audience. Aida and Radames sing their "Farewell to earth," and prayers are offered by Amneris.