In 1943, a shocking explosion in Shanghai results in a confrontation between Communist Party undercover Lu Zheng Yang and former police officer Lin Shao Bai, each flaunting their skills. Six years later, Shanghai is liberated, and Lu Zheng Yang becomes a core member in the anti-espionage efforts of the Shanghai Public Security Bureau. Faced with severe retaliation in their anti-espionage efforts, with the support of his superior and strict screening, Lu Zheng Yang boldly employs the former police officer Lin Shao Bai, the "Shanghai Expert". The two team up and successively solve major cases such as the "Treasury Robbery", "Counterfeit Coin", and "Hidden Radio" planned by the veteran spy Zheng Lan Ting of the Shanghai Secret Services’ Special Station, completely thwarting the conspiracy of the hidden enemy agents. Working on cases together, Lu Zheng Yang and Lin Shao Bai go from constant friction to gradually building trust, and eventually becoming comrades who live and die together.