The Devil is released into the human world and soon opens a door into a parallel world. The Devil asks if he lived a better life in the other world, if he could live in the other world. Against the Devil's question, Korean Emperor Lee Gon tries to close the door to the parallel world and South Korean Detective Jung Tae Eul tries to protect the lives of people and the person she loves.
E1
Lee Gon mourns the tragic death of his father. Lee Lim goes on the run - and finds escape when he comes across a door to a parallel universe.
E2
Gon insists he's an emperor from another world. An incredulous Jeong Tae-eul takes him to the police station, where he sees a familiar face.
E3
Though Tae-eul finds Gon's story difficult to believe, some things about him are completely inexplicable. At work, she gets busy with a murder case.
E4
When Tae-eul loses her police badge, she can't help but think about Gon. Meanwhile, Kang Sin-jae has had it with his mother's bad habits.
E5
Being introduced to Gon's world is a lot to process for Tae-eul, who's taken to the palace. A disgruntled Jo Yeong keeps an eye on her.
E6
A potential military conflict theatens the kingdom. Gon promises Tae-eul he will return to her, and steps forward to take care of the situation.
E7
Gon brings Yeong along on his trip back to Tae-eul. He has a favor to ask of her, while she's found something troubling to share with him.
E8
In Corea, Luna is set free. In Korea, Gon and Yeong run into a man who recognizes them, and Sin-jae experiences childhoos flashbacks.
E9
Gon draws closer to tracking down Lim, and asks Jo Eun-sup to trade places with Yeong. Mail from an unknown sender bothers Koo Seo-ryeong.
E10
On Lunar New Year, Gon and Lim come face-to-face in a public standoff. Tae-eul opens up to Sin-jae about the other world and her ongoing case.
E11
A compelling offer finds its way to Luna. Gon's investigation into a devastating murder leads him to an old traitor and a clearer idea of Lim's schemes.
E12
Frightening circumstances land Tae-eul back in Gon's arms. When Yeong runs into a woman who looks strikingly familiar, he follows her.
E13
Knowing Seo-ryeong is up to no good, Gon throws her in a tight spot. Upon returning to her wordl, Tae-eul realizes Luna is there, too.
E14
Gon and Tae-eul are separated when he sets out to fulfill what's been his fate all along. Sin-jae makes a startling discovery.
E15
Lims plots his next meeting with Gon. Understanding there's only one thing he can do to right wrongs, Gon comes to a heart-wrenching decision.
E16
A final attempt to put a stop to Lim's ambitions comes with profound consequences. Gon travels far and wide in search of Tae-eul.