Kanako, married to a man much older than her, had built a happy family life with Kazuo, her husband's stepson. However, due to his age, her husband could no longer satisfy her in the bedroom, leaving Kanako frustrated and longing for intimacy. Gradually, her feelings begin to shift toward Kazuo. One night, while washing his back in the bath, Kanako gathers the courage to make a bold advance—crossing the line into forbidden desire.