Lin Xi, a member of a dockside gang, finds himself unintentionally caught in an intelligence war between the Bureau of Investigation and Statistics (BIS) and Japanese invaders due to a key. Alongside his good friend Li Yunfei, they cross paths with Su Nan, a forward-thinking student, and Zhou Yingqun, an upright and principled BIS agent. As the enigma surrounding the key gradually unravels, it sets off clashes among gangs and sparks nationwide turmoil. Amid the turmoil, Lin Xi, Zhou Yingqun, and Li Yunfei form a profound brotherly bond, navigating through life-threatening scenarios.