In 1943, an explosion in Shanghai leads to the first showdown of skills between Lu Zheng Yang, a member of the Communist underground, and Lin Shao Bai, a policeman. With the liberation of Shanghai six years later, Lu Zheng Yang who becomes part of the public security bureau recruits Lin Shao Bai after rigorous screening. The two team and successively crack major cases in an effort to defeat enemy agents hiding in the dark. The two go from being constantly at odds to comrades-in-arms who trust each other with their life.