The younger sister, who is married to a playboy couple, complains that her husband's only good point is that he's serious, but she's not satisfied with him, so she proposes to her older sister that they swap spouses. The younger sister can't refuse, so she accepts the younger sister and her husband when they come to visit her house, and the younger sister begins to seduce her husband... The older sister is confused and jealous by the sight of her husband, who she has never seen before. Then, as the younger sister's husband attacks her, she gradually begins to feel aroused by the forceful way he embraces her, which is different from how he embraces her husband... She feels so much guilt and pleasure at being held by another man in front of her husband that she writhes in agony, accepting the other man's dick and sperm and climaxing!