Ryoko, whose marital life with her husband is not going well, has affairs with various men every Friday during the day when her husband and son-in-law are not around. However, Ryoko's son-in-law, Kiyoshi, who knows Ryoko's obscene secret, was always looking into such a mother-in-law. Feelings for mother-in-law gradually increase .... And Kiyoshi's desire exploded...