A serial killer who only appears on rainy nights has caused panic among the citizens. He has committed numerous crimes, and hundreds of police officers have been tracking the whereabouts of the murderer, but to this day, the true identity of this cold-blooded and cruel murderer remains a mystery. This time, the responsibility of investigating the case fell on the shoulders of the police officer Chang Min (played by Kim Dong-wook). However, Chang Min is a waste who has no requirements for himself and muddles through everything. It is probably impossible for this case to be solved in his hands. The slow progress of the police in solving the case has aroused the dissatisfaction of the people. They gathered in front of the police station to protest and demonstrate, and Chang Min's mother was among them. In order not to disappoint his mother, Chang Min decided to cheer up and thoroughly investigate the case. At this time, an unemployed vagrant named Rong Shi (played by Liu Wuxing) mixed in the investigation of the case, repeatedly taking Chang Min one step ahead to solve the incident, which made Chang Min very annoyed.