Dadan (played by Cheng Kuian) led a group of bandits to rob the South African Diamond King. They found the middleman Li Yunfei (played by Chen Huimin) to sell the stolen goods, but they shot and killed the buyer during the transaction. Li Yunfei took advantage of the chaos to escape. Undercover Zhang Lang (played by Zhou Xingchi) had a deeper and deeper misunderstanding with his girlfriend Zhou Wenli (played by Zhou Huimin) due to the special circumstances of his work. Zhang Lang wanted to quit, but under the pressure of his old boss, Officer Li (played by Danny Lee), he had to approach Li Yunfei in order to find out the diamond robbery. At that time, Li Yunfei was being hunted by Dadan's group. Zhang Lang helped him escape and gained Li Yunfei's trust. In the contact, Zhang Lang gradually discovered that Li Yunfei, as an old-school Jianghu figure, acted with affection and righteousness, and the two became brothers with different surnames. On the other hand, Zhang Lang has tried hard but failed to reveal his undercover identity to Li Wen, who is about to fake a marriage and go to Canada. Zhang Lang's superior in the police station only sees Li Yunfei as bait to lure him to show up. Zhang Lang is torn between his duty and friendship...