Chief Inspector Liu Zhengxi (played by Tony Leung Chiu Wai) and his wife Jin Shuzhen (played by Xu Jinglei) live a sweet life. Qiu Jianbang (played by Takeshi Kaneshiro), who was originally a colleague and friend of Liu Zhengxi, became a private detective after being dismissed from his police position. He drank all day until he was drunk. He could not forget the suicide of his girlfriend many years ago, and his relationship with the bartender Xifeng (played by Shu Qi) was complicated. Jin Shuzhen's father, the wealthy Jin Yuansheng, was suddenly murdered, and the spearhead pointed directly at two unemployed vagrants, but the suspect was also killed a week after the incident, and the police quickly closed the case. But Jin Shuzhen felt that there were many doubts in the case, so she asked Qiu Jianbang for help. As the case was gradually unraveled, unexpected secrets were discovered, as well as the culprit who deliberately set fire to try to kill Jin Shuzhen. How many secrets are hidden in a sad city?