The Devil’s Classroom, Loan Shark Ties, Private Debtors,A Private Debt, 사채지간 Kim Sang-an, a cold-blooded loan shark. When his sister, a school teacher, takes her own life after being relentlessly tormented by her students… He becomes their new homeroom teacher to collect the “debt” of her life. A debt collector who would crawl into the depths of hell to get what’s owed, and students who are nothing short of demons. A brutal “teacher-student” relationship begins now.