The series takes place in two different parallel worlds. A demon that has been unleashed in the human world is trying to transition to another parallel world. In response, Korean Emperor Lee Gon (Lee Min-Ho) strives to keep the doors to the parallel world closed. In another parallel world, Detective Jung Tae-Eul (Kim Go-Eun), living in the Republic of South Korea, works to protect the lives of people and their loved ones.
