Mako, who lost her husband, began living with her daughter and son-in-law. One night, she witnessed her son-in-law, who had been coldly treated by her daughter, masturbating in the bathroom. Excited, Mako masturbated in her futon, but this time she was caught by her son-in-law. On Sunday, when her daughter went shopping alone, Mako again saw her son-in-law masturbating. To the bewildered Mako, her son-in-law confessed his feelings for her. Unable to suppress their mutual lust, the two had a relationship. From that day on, their forbidden acts gradually grew more intense. Tormented by guilt, Mako nevertheless yielded to her son-in-law's passion and once again gave in to their physical union.