Kang Bit Na is a stunningly beautiful elite judge, but she is a demon. Her mission as a demon is to kill evil people who cause the deaths of others and show no remorse for their actions. She then sends these people to hell. One day, Kang Bit Na meets Han Da On. He has a friendly and kind personality. As a detective, he has a sharp mind and keen powers of observation. But he harbours a pain that nobody knows about. After Kang Bit Na and Han Da On meet, their lives change dramatically.