A man (Ki Tae-yeong) is imprisoned for murdering his father, a woman (Han Soo-jeong) is given a terminally ill life, Song Jang-soo (Park Cheol-min) stands at the edge of the cliff to end his life and ...

羅大起在高中時期曾是威名遠播的少年幫派老大，連其他學校的混混都不敢招惹他。升學後，大起毅然解散幫派、進入大學苦讀取得教師資格，並在畢業之後來到了充滿麻煩份子的「江湖高校」任教，很快就和不良少年起了衝突。學校裡的流氓老大知道新老師過去的名聲，開始挑釁大起，卻沒料到這位「資深前輩」早就準備好要給他們一場震撼教育......