Shiori, a married woman living with her husband and daughter, finds herself dissatisfied with their sexless life. One day, she accidentally catches a glimpse of her son-in-law masturbating, revealing an enormous penis that captivates her heart. Unable to resist its allure, she becomes obsessed with teasing him at every opportunity, even when he's tired from being neglected by his wife. Eventually, her son-in-law can no longer contain himself and gives in to his desires, seeking comfort in her naughty advances. As they continue their illicit relationship behind closed doors, both find solace in each other's company, leading them down a path of forbidden pleasure.

夫と娘夫婦の4人で暮らしている翔子。穏やかな生活ではあるが、夫とはセックスレスで物足りない日々を過ごしていた。そんなとき、偶然にも娘婿・敏夫の自慰を目撃してしまい…、暗闇に浮かぶ彼のあまりにも巨大な肉棒に心奪われた翔子。我慢できずに四六時中、場所を選ばす誘惑するのだった。妻とご無沙汰で悶々としていた敏夫は、堪らず義母の痴態に飛びつき、いつしか彼女との行為を心待ちにするようになり…。