Peking, in the mythic past. Outside the Imperial Palace, a mandarin reads an edict to the crowd: Any prince seeking to marry Princess Turandot must answer three riddles. If he fails, he will die. The most recent suitor, the Prince of Persia, is to be executed at the moons rising. Among the onlookers are the slave girl Lių, her aged master, and the young Calāf, who recognizes the old man as his long-lost father, Timur, vanquished King of Tartary. Only Lių has remained faithful to him, and when Calāf asks her why, she replies that once, long ago, Calāf smiled at her. The mob cries for blood but greets the rising moon with a sudden fearful silence. As the Prince of Persia goes to his death, the crowd calls upon the princess to spare him. Turandot appears in her palace and wordlessly orders the execution to proceed. Transfixed by the beauty of the unattainable princess, Calāf decides to win her, to the horror of Lių and Timur. The three ministers of state, Ping, Pang, and Pong, appear and also try to discourage him, but Calāf is unmoved. He reassures Lių, then strikes the gong that announces a new suitor.
Within their private apartments, Ping, Pang, and Pong lament Turandots bloody reign, hoping that love will conquer her and restore peace. Their thoughts wander to their peaceful country homes, but the noise of the crowd gathering to witness the riddle challenge calls them back to reality.
In the royal throne room, the old emperor asks Calāf to reconsider, but the young man will not be dissuaded. Turandot arrives. She recounts the story of her beautiful ancestor, Princess Lou-Ling, who was abducted and killed by a conquering prince. In revenge, Turandot has turned against men and determined that none shall ever possess her. Trumpets then herald the beginning of the riddles. Turandot poses her first question to Calāf: What is born each night and dies each dawn? Hope, Calāf answers correctly. Turandot continues: What flickers red and warm like a flame, yet is not a flame? Blood, Calāf replies after a moments thought. Shaken, Turandot delivers the third riddle: What is like ice but burns, and if it accepts you as a slave, makes you a king? Tense silence prevails until Calāf triumphantly cries Turandot! The crowd erupts in joy, and the princess vainly begs her father not to give her to the stranger. Hoping to win her love, Calāf offers Turandot a challenge of his own: If she can learn his name by dawn, he will forfeit his life.
At night in the Imperial Gardens, Calāf hears a proclamation: On pain of death, no one in Peking shall sleep until Turandot learns the strangers name. Calāf is certain of his victory, but Ping, Pang, and Pong try to bribe him to leave the city. As the fearful mob threatens him to learn his name, soldiers drag in Lių and Timur. Calāf tries to convince the crowd that neither of them knows his secret. When Turandot appears, commanding Timur to speak, Lių replies that she alone knows the strangers identity and will never reveal it. Soldiers torture her, but she remains silent. Impressed by her fortitude, Turandot asks what gives Lių the strength to resist. It is love, she replies. When the torture intensifies, Lių tells Turandot that she, too, will know the joys of love. Then she snatches a dagger and kills herself. The crowd forms a funeral procession, and Timur follows as they take away her body. Turandot remains alone to confront Calāf, who impetuously kisses her. Knowing emotion for the first time, Turandot weeps. Calāf, now sure of winning her, reveals his identity.
Once again before the emperors throne, Turandot declares she knows the strangers name: It is Love.