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.

The renowned hitman, ‘Flying Dagger,’ bumps into ‘Wild Dog,’ who happens to be a hired assassin for the mobster, ‘Black Leopard.’ While both of them try to be incognito, they cannot help falling in love with each other. However, ‘Wild Dog’ has a secret that he couldn’t confide to ‘Flying Dagger.’ After all, ‘Flying Dagger’ and ‘Wild Dog’ reveal their secret identities to each other during the fight led by their bosses. They run into danger as gangsters brand them as traitors. Will they be able to overcome obstacles and keep their love?