Kim Sang-an is a ruthless loan shark known for showing no mercy. But after his older sister—a gentle school teacher—ends her own life due to the constant abuse and harassment from her students, everything changes.
Determined to make them pay for the life they stole, Sang-an takes her place as the class’s new homeroom teacher. For a debt collector willing to descend into hell to recover what is owed, these students are simply another target.
Between a merciless collector and a classroom filled with monsters disguised as teenagers, a savage and twisted teacher-student conflict is about to unfold.