Mami, a married woman living with her husband and father-in-law. Her husband is always tired, and her father-in-law is cold and distant. Her brother-in-law, Keisuke, was the one who brightened up their gloomy lives. Though a playboy, he was a stimulating presence for Mami. Before she knew it, she fell for his charm and gave in to his advances. As she discovered the joys of sex and became immersed in it, one day, her father-in-law caught her in the act.