[Paul Robaix], a famous director, wants to film the Puccini opera on location in Japan under the title Madame Butterfly, with the dialogue spoken in English by the actors and the score sung in Italian by the best singers of opera available. His wife, Lucy Dell, has been the leading lady in all of his greatest films, and she is more famous. He feels that she overshadows him and he yearns to achieve success independent of her. By choosing to film Madame Butterfly, he can select a different leading lady without hurting her feelings, because she, as a blue-eyed, red-headed comedy actress, would not be suitable to play a Japanese woman in a tragedy. As a surprise, she visits him in Japan while he's searching for a leading lady. To surprise him further, she disguises herself as a geisha at a dinner party, planning to unveil her identity during the meal.
But she is delighted to discover that everyone at the dinner party, including her husband, believes her to be a Japanese woman. She learns that the studio has decided to give her husband just enough funds to film the movie in black and white, with inexpensive singers, because there are no big stars in the film. She decides to audition for the role of Butterfly with the studio's knowledge but without telling her husband. Then the studio will give him the budget he needs to make the film he wants.
Lucy Dell gets the part and is wonderful. Through the course of the film, she begins to be concerned that Yoko Mori will steal her husband's affections, though he never does develop feelings for the invented character.
When viewing the film's negatives, in which colors are reversed, he sees through her duplicity and, believing that she plans to steal credit from him, once again depriving him of the artistic praise he deserves, he becomes furious. To retaliate, he propositions Yoko. Greatly distressed, Lucy flees. He tells Sam Lewis that he has just learned the truth and makes him promise not to tell Lucy—or anyone. Their love affair is over. Broken hearted, Lucy gives a brilliant performance in the last scene, but she comes up weeping on Sam's shoulder.
Their "reunion" before the premiere is awkward and cold. Paul believes she will expose her identity there, betraying him, and Lucy believes that her husband wanted to sleep with Yoko. Her original plan was to come on stage as Yoko and pull off her wig at the end of the premiere, astounding Hollywood and virtually guaranteeing her an Academy Award. While the aria Un bel di, vedremo plays, Lucy goes backstage to put on her geisha costume. Kazumi gives her a present—an ivory fan that was owned by a very famous geisha. The fan is inscribed with a proverb: "No one before you, my husband, not even I." The film reaches its tragic ending and receives a standing ovation. Paul thanks the audience and introduces Yoko Mori. Lucy appears as herself and announces that Yoko has gone into a convent. They walk to each other across the width of the stage. As they bow to waves of thunderous applause, he calls her “my geisha” and she weeps tears of joy.
