During the Republic of China, Tianjin suffered frequent floods, and there were endless strange and supernatural things in the river. Guo Deyou, the captain of the river police team, learned the true teachings of his master, the "Old River God", and his unique skill of lighting a cigarette to identify injustice comforted countless innocent souls. The president of the Canal Merchants Association died strangely in the river. Guo Deyou was suspected and worked with the president's son Ding Mao and his childhood sweetheart Gu Ying to investigate the case. They found that the real murderer pointed to an event twenty years ago. At that time, a cult organization called "Mo Gu Dao" was raging in the Beijing-Hebei area. Twenty years later, Guo Deyou and Ding Mao found the traces of "Mo Gu Dao" again. In order to prevent the restoration of Mo Gu Dao, Guo Deyou, Ding Mao and Gu Ying were involved in a series of thrilling and bizarre cases.