Ancient Korea, 17th century. While the paranoid King Lee Jo of Joseon, vassal of the Qing dynasty, feels surrounded by conspirators and rebels, a dark evil emerges from the bowels of a merchant ship and the exiled Prince Lee Cheung returns to the royal court, ignoring that he will have to lead the few capable of defeating the ambitious humans and the bloody monsters who threaten to destroy the kingdom.

Chinese secret agent Da-hee receives intel that a large number of illegal firearms are being smuggled into Korea and is sent to investigate the case. She meets Su-han, who is supposed to help her with the case, but due to his lackluster skills they fight over trivial things. But as their witnesses are suddenly murdered, the two of them quickly become the prime suspects.