Kang Bit-na is a strikingly beautiful judge, but beneath her flawless exterior, she hides a dark secret — she is a demon. Her mission is to hunt down and kill evil people who lead other people to their deaths and don't reflect on their actions and are unforgivable. After executing her judgment, she condemns their souls to Hell. However, her life takes an unexpected turn when she encounters Han Da-on, a detective with a warm and gentle demeanor. As a detective, his mind is sharp and he has a keen sense of observation. Despite his outward kindness, Han Da-on harbors deep, unseen pain. Their meeting sets off a series of events that profoundly alters both of their lives.