Lee Gon, the third-generation emperor of Korea, is admired as the perfect ruler—but behind his composed image lies a painful past. As a child, he witnessed his father's murder during a coup. Now an adult, he often escapes royal duties to attend university lectures. During one of these outings, he’s transported to a parallel world where he meets Jeong Tae Eul, a determined detective. Together, they join forces to fight crime and seal the gateway between their two worlds.