The young doctor had to read a letter every single day from the serial killer. It was always the same, addressed from the same maximum security prison, with the same content. What it felt to kill the doctor’s father. For years, he would grip each new letter and re-traumatize himself. He became a shell of a man. For years, the killer thought he was winning. Sure, he was behind bars but he was slowly killing the victim’s son mentally. That was all that mattered. But through a series of seemingly random events the serial killer was transferred to one of the toughest prisons in South Korea. The ultimate maximum penitentiary. He didn’t know what was going on… but he knew it was no coincidence when he came face to face with the prison doctor. The son. What does he have in store for the killer? How will he get revenge inside the prison walls?