A young Japanese girl, Cio-Cio-San of Nagasaki, decides to marry Lieutenant Pinkerton of the American Navy, the man she loves. Pinkerton sees this marriage as a short-lived adventure, whereas Cio-Cio-San's love knows no boundaries; she cares not if she sacrifices all her Japanese roots and traditions for the sake of her happiness.
As the opera starts, the marriage broker Goro is showing Pinkerton round the home he will share with Butterfly. The American Consul, a man with adept knowledge of Japanese traditions, warns Pinkerton about the tragic consequences his game could have, but Pinkerton is a selfish, stubborn man and chooses to ignore the warning. Butterfly arrives and introduces him to her relations.
The marriage ceremony begins. The young people adorn the bride. The unexpected appearance of her uncle Bonze unnerves the guests; he utters blasphemies against the girl who has denied the ancient customs and leaves taking all the guests with him.
As night fall the two lovers, alone at last, sing of their love binding them together into a serene and endless happiness.
Cio-Cio-San lives with her devoted friend and servant Suzuki. Pinkerton has left the country promising to return in one year. Three years later, he has still not returned. Cio-Cio-San gazes sadly over the sea in the hope of seeing his ship. One fine day, she says, they will be reunited. Consul Sharpless brings her a letter announcing the expected arrival of an American ship, but he does not have the heart to tell her Pinkerton has remarried, especially when she introduces him to her and Pinkerton's son. In her joy Cio-Cio-San asks Sharpless to write a letter to her husband expressing her happiness at his return. . A cannon announces the ship's arrival and wipes all doubts from Cio-Cio-San's mind. Happily she embellishes her house with flowers as she counts the minutes to his arrivalâ€¦
Night-time; Suzuki and the child sleep, and only Cio-Cio-San is awake, listening to the Marines' chorus whilst she expectantly waits for Pinkerton's return. Exhausted, Cio-Cio-San retires to her bedroom. Meanwhile Sharpless and Pinkerton enter the house. In the garden waits Pinkerton's new, American wife Kate.
Suzuki is asked to explain to Cio-Cio-San that Pinkerton wishes to take her child away with him and his wife. Having heard the voices, Cio-Cio-San appears filled with happiness at the sight of her husband, but seeing Suzuki's solemn face, she realizes the true intentions of his visit: to take away her child. The child is separated from his loving mother, who, distraught, kills herself.