The protagonist, Youta, has a woman whom he trusts and respects the most―― His mother, Kawachi Shiori. Unlike his workaholic father who doesn't care about his family, Shiori is very family-oriented and has been fond of Youta for a long time. In contrast to her husband who is always on long-term​ business trips, Shiori has been taking care of their house and Youta without any complaint. In her heart, however, she is tormented by stress due to her loneliness and not being able to have sex anymore. Occasionally, with deep sigh and gloomy look on her face, Youta worries about his mother, but couldn't find the words to say to Shiori who always acts courageously. At such time, Shiori went shopping in the shopping district and met her former teacher who took care of her when she was a university student―― Sakashio Masao. Aiming for his former student, Sakashio harbours an evil thought...... Without noticing her teacher's rear side, Shiori inadvertently invited him to her house. Recognizing Sakashio as a "good and caring teacher", Shiori served him tea and consulted with him about her painful feelings made by the gap between her and her husband. Sakashio, who is infatuated with his former student, in order to get his hands on her this time, gave consultation about her worries, entered the gap in Shiori's heart, and approached her. Suddenly, Sakashio began to touch the private parts, Shiori was surprised by his action, but couldn't strongly reject her former teacher who used to take care of her, and let him gradually embraced her. After being hugged, Shiori felt regret for betraying her family. While carefully caressing Shiori's body, Sakashio offered to continue the physical relationship. Thinking that she shouldn't do such a thing, Shiori refused the offer, however, in front of Sakashio who could satisfy her starving desire, Shiori later accepted the offer. Since then, during the day, when Shiori's husband and Youta are not around, Sakashio began to visit Shiori's house and had his way with her mature body. Since Shiori didn't refuse his offer, Sakashio also invited his own son and his friend, Jack, and the three of them had sex with Shiori...... Thus began a group sex. Shiori was uncomfortable and resisted having sex with Jack and Sakashio's son, Masafumi, but due to her unusually strong sexual desire, when the pe*is is inserted, she would soon let out the sound of pleasure. Her family...... Especially her son, Youta, must never know that she is allowing men other than her husband to have their way with her body. Shiori thought so, however, when Youta, who had to leave the school early due to poor physical health, witnessing a woman being held by Sakashio in the bedroom. "Mom is cheating? That can't be true." Youta told himself, not his usual kind and solid mother, but he was fascinated by the sight of her moaning with pleasure. After seeing Shiori's mature body, Youta became aware of her not as a mother, but a woman, and began to masturbate using his mother as a material. Unaware that Youta has found out her secret, Shiori lost herself to lust with Sakashio and his friends. Starving for desire, a lonely mother, Shiori. Tormented by the fact that he now sees his mother whom he respects, as a woman, Youta. Toying with a parent and a child, harbouring an evil thought, an adulterer who entered a house when the husband is not around, Sakashio. Drowning in lust, the story of a pitiful mother and a son falling into the depths begins. [Translated and edited from the official website]