After being struck by a meteorite a year ago, Jiang Bei acquired the "Demon King's Heart," which allows him to devour supernatural entities and gain their abilities. Down on his luck and struggling in poverty, he joins Bureau Nine as an assistant to his childhood friend Wang Xue, secretly devouring supernatural entities to help her rise through the ranks and become a legendary investigator. Liu Piaopiao, the bureau chief, is hostile toward Jiang Bei because of her father's loss of control as a successor to the Demon King, and has him taken into custody. Meanwhile, Yu Luosha, the ruler of the underworld, plots a new supernatural incident and opens the Gate to the Underworld in an attempt to invade the human world.