In Republican Shanghai a handsome monster hunter Yu Wen seeks for another beast in the Grand Hotel. When the monster attacks Gu Qing, Yu Wen surrenders from the sky and interrupts the public confession of a wealthy detective, Tian Ming. The three of them are involved in a series of supernatural cases. All the clues point to a legend - the beast has returned to earth and a mysterious manipulator has surfaced....

A hundred years ago, the Demon Lord controlled the world and nobody could stop him. Later, the fish-like people sealed off the Demon Lord in order not to let him harm the world. The elders of the clan formed several battle arrays with the strength of the whole clan, and sacrificed themselves as guardian gods of arrays. Fearing that later generations would awaken the Demon Lord, the fish-like people built an island at the entrance of the arrays to guard him from generation to generation. Thousands of years later, the strength of the arrays gradually declined and the arrays were broken. Demons began to appear around the world. Several pieces of the remaining soul which escaped when the Demon Lord was sealed invaded the host constantly and the Demon Lord used them to help him break the arrays and re-emerge in the world.