The setting is Nagasaki in the Meiji Era. The U.S. naval officer Pinkerton buys the freedom of 15-year-old Cio-Cio-San in Nagasaki, where his ship docked, and marries her without giving it too much thought. Pinkerton soon departs for America. Despite his long silence, Cio-Cio-San waits for her husband's return in the belief that "one fine day he will come back" and turns down a new proposal of marriage. Finally Pinkerton's ship calls at Nagasaki again. But he is accompanied by his wife Kate. Having seen an unfamiliar American woman and learned the whole truth, Cio-Cio-San kills herself with a dagger left by her father.