In a turbulent time in the Ming Dynasty, the Imperial Bodyguard solves humans’ cases, while the Jinwu Guard takes charge of ghosts’ and monsters’ business. Eunuch Wei seizes great power and suppresses dissidents. Colluding with the monster Huo Feiyuan, he framed up Feng Tingzhang, the Director of the Grand Court. Zuo Changgeng, Feng’s disciple, accidentally gets involved in the Jinwu Guard’s monster hunting as he investigates the treasury’s theft case. Though despising the Jinwu Guard, Zuo Changgeng has no choice but to ask the Jinwu Guard for help to save his master. Yi Shuihan is an upright half-human and half-monster member of the Jinwu Guard. Zuo and Yi work together and investigate in the humans’ and monsters’ worlds, before they gradually see through Eunuch Wei’s intrigue. But the Jinwu Guard is framed up and then controlled by Eunuch Wei, and Yi and Zuo fall into Huo’s trap. It turns out that Huo is the mastermind behind everything to destroy the Qianyuan Formation that suppresses the monster world and release monsters to the human world. Yi and Zuo cooperate and defeat Huo, but Eunuch Wei takes the merit of killing monsters and rescuing the Emperor, because of which he becomes domineering in the court. Seeing the chaotic world, Zuo and Yi leave the court and wander around to pursue peace of their own.