US Navy Lieutenant Pinkerton is stationed in Nagasaki, Japan. He has paid for an arranged marriage with a fifteen-year-old geisha, Cio-Cio-San, known as Madam Butterfly. As the action begins, Pinkerton is with Goro the marriage-broker. A few minutes before the wedding is to take place, the US consul Sharpless arrives. He tells Pinkerton that he is convinced Butterfly is deeply in love. He fears that Pinkerton will destroy her as he does not take the marriage seriously, but regards it merely as a convenience. Pinkerton dismisses his fears but affirms that he waits for the day he will make a ‘genuine’ marriage to an American woman.
Butterfly arrives with her friends. She charms with her cultivated manners and child-like appearance: she is from a noble family that has been reduced to penury, and has had to earn a living as a geisha. It emerges that her father committed suicide at the request of the emperor.
The remaining wedding-guests and officials arrive and a simple ceremony takes place. As the toasting begins, the voice of the Bonze – the high-priest – is heard. He reveals that Butterfly has converted to Christianity. He and the entire Japanese contingent renounce her. They disperse, shouting curses as they go.
Pinkerton tries to comfort Butterfly. Suzuki, her faithful servant, prepares her for the night. The newly-weds are left alone. Darkness has fallen, the sky is full of stars.
Three years have passed. Pinkerton left Nagasaki soon after he ‘married’ Butterfly, promising that he would return in the spring ‘when the robins nest’. Butterfly and Suzuki are on the verge of destitution. Suzuki tries to make Butterfly see that Pinkerton will not return, but she is determined to wait for him.
Sharpless visits with a letter from Pinkerton. He tries in vain to read it through Butterfly’s constant chatter. They are interrupted by Goro and Prince Yamadori, her rich suitor. She has rejected his offer of marriage many times and does so again, insisting that she is already married. Goro points out that, under Japanese law, deserted women are automatically divorced. She is American, she says, and will only recognise American law. The two leave Sharpless and Butterfly alone. He resumes his attempt to read the letter. It is clear that Pinkerton has asked Sharpless to tell her that he will not be returning. Sharpless tries gently to guide her towards facing the truth and suggests she should accept Yamadori’s proposal. She produces her trump-card: she has borne Pinkerton’s son. Surely he will not forget her now? Sharpless, at a loss, leaves her to her waiting.
A cannon-shot is heard from the harbour. Pinkerton’s ship has returned.
Butterfly has waited all night, but Pinkerton has not come. Suzuki persuades her to rest. Sharpless arrives with Pinkerton hoping to find Suzuki alone. She must be the one to explain to Butterfly that Pinkerton has an American wife, Kate, and that they wish to adopt the son that Butterfly bore him. Pinkerton is aghast at what has happened and leaves Sharpless and Kate with Suzuki. Butterfly bursts in on them and unable to live with the truth, she commits suicide.