In 1994, the Kingdom of Corea encounters severe upheaval. The King (Kwon Yool) is murdered by his brother Lee Lim (Lee Jung-Jin) and the King's son Lee Gon (Jeong Hyun-Jun) is stabbed in the neck, but he survives. The murderous Lee Lim seeks to possess the Manpasikjeok, which is legendary flute that holds supernatural powers. After a mysterious figure appears with a gun, Lee Lim slips away with only half of the now broken flute. The young Lee Gon holds onto a police badge he grabbed from the mysterious figure. The next day, Lee Goon is appointed the next ruler of the Kingdom of Corea.
25 years later, in the autumn of 2019, King Lee Gon (Lee Min-Ho) governs the Kingdom of Corea as its benevolent leader. He is still haunted by what happened when he was a child and the mystery behind the police badge left by his savior. The police badge he held was issued on November 11, 2019 for Lieutenant Jeong Tae-Eul.
Autumn 2019, in the Republic of Korea, Jeong Tae-Eul (Kim Go-Eun) is a detective in the Violent Crimes Division at the Seoul Jongo Police Station. She is working undercover to takedown the operator of an illegal online gambling operation.
Meanwhile, in the Kingdom of Corea, King Lee Gon chases after someone that is dressed like a rabbit with a clock. King Lee Gon has a feeling that the person dressed like a rabbit may be his mysterious savior from 25 years earlier. King Lee Gon mounts his horse Maximus and enters the forest. Soon, he crosses over from the Kingdom of Corea into the parallel world of the Republic of Korea. King Lee Gon finally meets Detective Jeong Tae-Eul.
