Sayo, a married woman living with her daughter and son-in-law in an apartment, is an ordinary housewife with a distant, unsatisfying relationship with her husband. One night, her son-in-law catches her masturbating, captivated by the alluring figure of his stepmother-in-law. He forcefully makes her give him a blowjob, and Sayo experiences pleasure for the first time. The next day, he coerces her into sex, and she gradually becomes drawn to his body, beginning an intense affair. As she develops new emotions unlike anything before, Sayo starts seeking the thrilling pleasure that contrasts sharply with her mundane life with her husband.