ひとり息子が今秋に結婚する予定で婚約中の女性みゆさん。結婚前の仲睦まじい若い男女は、週末になると、市内の式場へと、披露宴やら引き出物やらの打ち合わせだと言っては、楽しげに通う日々を送っていた。そんな「倅のおフィアンセ」の若く瑞々しい女体隆起をじっとりとした陰湿な視線でいつも見つめている義父。ある日息子がみゆさんを残して仕事へと出掛けていった日、義父は年甲斐も無く恥ずかしい程に固く勃起した逸物を…！

Miyu is engaged to her only son, who is getting married this fall. The young couple, happily in love before their wedding, spend their weekends going to a wedding hall in the city, supposedly to discuss the reception and wedding favors. Meanwhile, her father-in-law always stares at his son's fiancée's youthful, voluptuous body with a lustful, sinister gaze. One day, when her son left for work, leaving Miyu behind, the father-in-law's penis, embarrassingly hard and erect for his age, became aroused…!