Hu Zhian was once an ordinary investigator. After absorbing the power of the Niehun Pearl, his physical body transformed into a spirit form, allowing him to defeat the mysterious man and quell the Ghost Gate incident. However, his life-and-death brother, Kuaike, turned to darkness and fell into the Ghost Gate. Twenty-seven years have passed. Having become a spirit, the memories of those around him have faded, and he has changed his name to Guyue, continuing to hunt evil spirits and maintain the balance between yin and yang. By chance, Guyue discovers a diary left behind in Kuaike's home, detailing the rise and fall of the four great families of the Medicine King Shennong, with Kuaike's ancestors and the mysterious man also listed among them. He immediately launches an investigation. Later, Guyue encounters two descendants of the Medicine King lineage. This meeting sets the wheels of fate rolling once more—a long-distant massacre of an entire family, hidden histories buried in dust, the resurgence of demons and monsters, and a conspiracy spanning over a hundred years. Amidst the surging undercurrents, when the most trusted person becomes an enemy, how will Guyue choose?