Zhao Yunlan, a detective of supernatural phenomena, is tasked to investigate mysterious cases with expert professor, Shen Wei. As they uphold peace between creatures and humans, Yunlan realizes there is more to Shen Wei than meets the eye.

A peace that has lasted over 10 000 years - between humans, Yashou and Dixing - is under threat when a series of events start to unfold on the planet of Haixing. Dixing people, who normally lives underground, suddenly start causing trouble on the surface with their special abilities. This is all somehow connected to four ancient holy tools. Zhao Yunlan is the unruly director of the Special Investigation Department (SID) who is put in charge of investigating these unusual cases. When things start happening at the local university a calm and gentle professor by the name of Shen Wei becomes involved with helping SID solve these cases. Not only does Shen Wei agree to help, repeatedly, but he also seems to know more about everything than he lets on. Also working with SID is a leaders from Dixing, the Black Cloaked Envoy, who upholds justice and helps keeping the peace. Although, when a formidable enemy starts moving behind the scenes it becomes harder and harder for SID and their allies to keep the world from being swallowed completely by the darkness. Along the way, an old promise is kept and a friendship between two guardians develops to transcend both past and present lifetimes.—Xiao Guo