Reiko travels to a hot spring resort with her beloved son. To outsiders, they appear to be a close mother and son, but in reality, they are engaged in a forbidden relationship—and this trip is meant to deepen their illicit bond. After arriving at the inn, they head to a private family bath. The son enters the tub first, while Reiko follows shortly after. A man watching from the side turns to his companion and says, "She's a fine woman. Let's go peep," and the two secretly tail Reiko. Inside the bath, her son is already waiting. Apologizing for her delay, Reiko immediately moves close to him, sharing passionate kisses as they indulge in their incestuous love. The two men, shocked by what they see, begin secretly recording them. That night, one of the men approaches Reiko under false pretenses, shows her the recorded footage, and begins blackmailing her. Though she appears strong-willed, Reiko is powerless against him and is soon forced into submission. Still emotionally shaken, Reiko tries to enjoy dinner with her son, savoring their time together. But suddenly, the men reappear. The innkeeper informs her she must come out immediately—left clueless about what awaits her, Reiko obediently follows, with no choice but to face the unknown.