Shoko shares a home with her husband, daughter, and son-in-law. Life is peaceful, but a sexless marriage leaves her deeply unsatisfied. Then she accidentally sees her son-in-law Toshio masturbating and becomes mesmerized by the enormous cock rising in the darkness. Unable to resist, she starts tempting him everywhere at all hours. Toshio is frustrated from going without sex with his wife, so he eagerly falls for his mother-in-law's shameless displays and soon begins looking forward to every forbidden encounter.