Mariko, a PTA officer at her son's middle school where he attends, finds herself involved in organizing a school festival along with other parents and teachers. After a successful first meeting at a local izakaya, they move onto karaoke for round two. Amidst all the fun, Mariko sets her sights on her son's teacher, lusting after his experience and maternal instincts. She begins teasing him intimately until eventually they embark on an affair...

長男が通う中学校でPTAの役員を務めるまりこ。ある日、会長の提案で担任も含め学園祭の打ち上げをすることになった。一次会の居酒屋で盛り上がり、二次会のカラオケへ。そんな中、欲求不満なまりこは長男の担任に目を付ける。 年上の経験と母性を活かして密着誘惑。やがて二人は不倫関係に...。