In a quarter swarming with people near the Forbidden City, a Mandarin reads an edict: any prince seeking to marry Princess Turandot must answer three riddles - and if he fails, he will die. Her latest suitor, the Prince of Persia, is to be executed at the rise of the moon. Bloodthirsty citizens urge the executioner on, and in the tumult a slave girl, Liù, calls out for help when her aged master is pushed to the ground. A handsome youth recognizes him as his long-lost father, Timur, vanquished king of Tartary. When the old man tells his son, Prince Calàf, that only Liù has remained faithful to him, the youth asks her why. She replies it is because once, long ago, Calàf smiled on her. The mob again cries for blood, but the moon emerges, and all fall into sudden, fearful silence. The doomed suitor passes on the way to execution, moving the onlookers to call upon Turandot to spare his life. Turandot appears and, with a contemptuous gesture, bids the execution proceed. The crowd hears a death cry in the distance. Calàf, smitten with the princess' beauty, determines to win her as his bride, striding to the gong that proclaims the arrival of a new suitor. Turandot's ministers Ping, Pang and Pong try to discourage the youth, their warnings supplemented by the entreaties of Timur and the tearful Liù. Despite their pleas, Calàf strikes the fatal gong and calls out Turandot's name.

 

In their quarters, Ping, Pang and Pong lament Turandot's bloody reign, praying that love will conquer her icy heart so peace can return. As the populace gathers to hear Turandot question the new challenger, the ministers are called back to harsh reality.

 

The aged Emperor Altoum, seated on a high throne in the Imperial Palace, asks Calàf to give up his quest, but in vain. Turandot enters and tells the story of her ancestor Princess Lou-Ling, brutally slain by a conquering prince; in revenge Turandot has turned against all men, determining that none shall ever possess her. She poses her first question: what is born each night and dies each dawn? "Hope," Calàf answers correctly. Unnerved, Turandot continues: what flickers red and warm like a flame, yet is not fire? "Blood," replies Calàf after a moment's pause. Shaken, Turandot delivers her third riddle: what is like ice but burns? A tense silence prevails until Calàf triumphantly cries "Turandot!" While the crowd gives thanks, the princess begs her father not to abandon her to a stranger, but to no avail. Calàf generously offers Turandot a riddle of his own: if she can learn his name by dawn, he will forfeit his life.

 

In a palace garden, Calàf hears a proclamation: on pain of death, no one in Peking shall sleep until Turandot learns the stranger's name. The prince muses on his impending joy; but Ping, Pang and Pong try unsuccessfully to bribe him to withdraw. As the fearful mob threatens Calàf with drawn daggers to learn his name, soldiers drag in Liù and Timur. Horrified, Calàf tries to convince the mob that neither knows his secret. When Turandot appears, commanding the dazed Timur to speak, Liù cries out that she alone knows the stranger's identity. Though tortured, she remains silent. Impressed by such endurance, Turandot asks Liù's secret; "Love," the girl replies. When the princess signals the soldiers to intensify the torture, Liù snatches a dagger from one of them and kills herself. The grieving Timur and the crowd follow her body as it is carried away. Turandot remains alone to confront Calàf, who at length takes her in his arms and makes her ice cold heart melt. The prince, now sure of his victory, tells her his name.

As the people hail the emperor, Turandot approaches his throne, announcing that the stranger's name is - Love.