「先生！後ろ！！」老化で聴力＆視力も反応も低下しているおじいちゃん先生。校内ではこの先生の授業中はサボってもバレない！と評判。そこでクラスの女子たちが悪ノリで授業中でも先生が後ろ向いているスキにエッチなこともイケるんじゃない？と授業中にもかかわらずギリギリでせめぎ合うドスケベなチキンレースを開催！最初はパンチラや胸見せ、キス…等の軽いレベル。しかし先生が全然気づかないと分かると、その行為はどんどんエスカレート！最終的には挿入まで決行する女子も…。バレたらアウト（即停学？）のスリルに女子のテンションはMAX！そして男子はその危険な遊戯に巻き込まれる。おじいちゃん先生はまさか自分の背後でセックスしているなんて夢にも思わない！しかも授業中に！

"Teacher! Behind you!!" The elderly teacher's hearing, eyesight, and reflexes have all deteriorated with age. It's said that you can skip class with him without getting caught! So the girls in the class, taking advantage of the situation, decide to have a naughty game of chicken while the teacher is facing away from them during class! At first, it's just light stuff like flashing panties, showing breasts, and kissing… But once they realize the teacher doesn't notice, their actions escalate! Eventually, some girls even go as far as penetration… The girls are thrilled by the risk of being caught (immediate suspension?), and the boys get caught up in this dangerous game. The elderly teacher has no idea that they're having sex behind his back! And during class, no less!