In the early 1990s, on the eve of the formation of Serious Crime Unit Six in Dong'an City, provincial detective Zeng Keqiang is transferred to the local major crimes unit for a special assignment. There, he takes over the unfinished investigation of his fallen colleague, Liu Hua. Burdened by suspicion and misunderstanding, Zeng struggles to earn the trust of his new team while secretly pursuing the truth. Meanwhile, a powerful criminal network is tightening its grip on Dong'an. Zhao Bin, heir to the Zhao Group, has built his empire through smuggling aboard sand-mining vessels, bribing officials, and violently eliminating his competition. To conceal his crimes, he begins systematically murdering anyone who knows too much. While Zeng infiltrates the organization from within, Ji Jie confronts its provocations head-on. As the members of Unit Six battle the Zhao Group, they also join forces to solve a string of extraordinary cases—including a serial bombing driven by revenge, a dismemberment case along the river, a staged resurrection linked to a mining-disaster insurance scam, a deadly seduction scheme, the Ghost Ship Massacre, and a highway carjacking involving a mysterious beauty.