The story takes place in a small town in the 1990s. The series of murders indicate that there is a vicious and cold-blooded serial killer lurking in this rainy city, and this person is very likely to be an insider in a local factory. Yu Guowei (played by Duan Yihong) is an officer of the factory security department. He is known as "Detective Yu" because he has solved many theft cases in the factory. After the murder, Yu Guowei felt that he had the responsibility to contribute to the investigation of the truth of the case. However, in the eyes of the criminal investigation team leader Lao Zhang (played by Du Yuan) and Officer Li (played by Zheng Chuyi), Yu Guowei was just a joke. Yu Guowei decided to investigate the truth of the case by his own strength, and met a woman named Yan Zi (played by Jiang Yiyan) by accident. A repressed and subtle relationship developed between Yu Guowei and Yan Zi.