A crowd has assembled inside the walls of Peking. The Prince of Persia is the most recent in a long line of suitors who have tried to solve the riddles set by Princess Turandot. Like those before him he has failed. All that awaits him now is death.
Imperial guards try to keep back the onlookers who jostle each other to get a better view of the execution. Among the crowd is an old blind man who, unable to move easily in such a crowd, stumbles and falls. The old man is Timur, who was once king of Tartary. Defeated in battle, he was driven from his land and now lives in exile. He feels strong arms embracing him. Chance has reunited him with his long lost son, Prince Calaf.
Timur tells Calaf of his long wanderings and of the devoted support he has received from his companion, a young slave girl, Liù. It is soon obvious that Liù is not only loyal to her royal master, but also deeply in love with his son. The happy reunion is interrupted. The servant of the executioner arrives.
When Calaf learns that Turandot is responsible for the deaths of so many young men, he is appalled. But when Turandot appears, his disgust for her turns to wonder. He is bewitched by her beauty.
Timur and Liù are quick to realise what Calaf is thinking. Surely he would not risk his life in an attempt to solve the riddles? The challenge would mean certain death. But Calaf's mind is made up. He feels certain that he can succeed - even though all before him have failed.
To signify that he is a suitor for Turandot's hand, Calaf moves to strike the great gong. Before he can do so, three Government ministers, Ping, Pang and Pong, block his way. "Don't be so foolish", they say, "It's an impossible task". But Calaf is determined, even deaf to the entreaties of his father and Liù (Signore, ascolta). Calaf consoles Liù (Non piangere Liù). Shouting the name "Turandot", he strikes the gong.
Ping, Pang and Pong meet to discuss the situation in China. People are tired of the endless round of executions. Ping, Pang and Pong long for their country houses: "Oh that we could retire and forget about Turandot's oath!"
Then eight wise men appear. They carry the scrolls which contain the solution to the riddles. Emperor Altoum begs the unknown Prince (Calaf) to refuse the challenge. 'Leave' he advises 'and live. If you accept the challenge, then death is certain'. But Calaf refuses to change his mind.
Turandot appears and explains the reasons for her cruel test (In questa reggia). She says that she believes she is the reincarnation of Princess Lo-u-Ling. No man will ever possess her. The riddles may seem a strange way to protect her from her suitors. But they never fail.
Calaf accepts the challenge and answers the riddles. Turandot is his. But, he asks himself, what is the point of winning her if I don't win her heart? So he suggests another test. 'You do not yet know my name' says Calaf. 'If you can discover it before sunrise you can treat me like the other suitors, I am not frightened to die'.
Calaf, the 'Unknown Prince', waits for the dawn. Turandot, who is determined to discover his name has decreed that no one may sleep until it is discovered. The prince echoes this order (Nessun dorma). Ping, Pang and Pong try to bribe Calaf to leave Peking and give up his plans to marry Turandot. His refusal to do so annoys them and infuriates the crowd. Suddenly the situation worsens. Timur and Liù have been held on suspicion of knowing the name of the 'Unknown Prince' (Tu che di gel sei cinta). They are dragged in and Turandot is summoned to confront them.
On learning that Liù can provide the name that will enable Tuarandot to remain unmarried, Turandot commands that the girl be tortured. Liù refuses to submit, explaining that she loves the 'Unknown Prince'. How could she betray him! Liù realises that to protect Calaf she must place herself outside the powers of her torturers. She kills herself.
Love of such intensity impresses even Turandot. Alone together Calaf challenges her to become human, to show love and affection. He kisses her and for a moment it seems as if she has changed. Calaf, as a sign that he trusts her tells her his name and so places himself in her power.
The Trumpet sounds. The court is summoned. Turandot faces her father, his courtiers and the people of Peking. Proudly she declares that she has discovered the name of the stranger.
'His name is Love'.
