The story takes place during the Republic of China. The southern metropolis of Decheng is a city full of sin. On this day, the police inspector Gong Sunze (played by Wang Kai) received a death notice from the "Blue Letter Man", and he hurriedly took people to the notice location. Zhao Xiaoman fell from the sky and died in front of the police. The forensic doctor Hu Xueli (played by Zhang Li) suspected suicide, but the prosecutor Bao Zheng (played by Zhang Duo) asserted that it was murder. At this time, Chen Shimei (played by Liu Mu), the son-in-law of the "Jiangnan Ship King", was killed in the bombing again, and Qin Xiaolian (played by Liu Yuxin), who came to Decheng to find her husband, became a suspect. A murder occurred in the antique shop, and Bao Zheng, Gong Sunze and detective Zhan Chao (played by Hu Yuwei) tried their best to solve it. Strange things have not been settled one after another. The newborn son Yangyang of Decheng Speaker Zhao Xun (played by Gao Shuguang) was replaced with a dead cat in the hospital. After many negotiations, they actually uncovered a shocking conspiracy of an illegal pharmaceutical group...