Kang Bit Na is an elite judge with a beautiful appearance, but she is a demon. Her mission as a demon is to kill evil people who lead other people to their deaths and don't reflect on their actions. She sends these people to Hell afterwards. One day, Kang Bit Na meets Han Da On. He has a friendly and gentle personality. As a detective, his mind is sharp and he has a keen sense of observation. But he carries pain inside that nobody knows about. After Kang Bit Na and Han Da On met with each other, their lives changed greatly.