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. Lin Xi develops affection for Su Nan and embraces communist ideals. Seven years later, the scattered trio reunites in Jinzhou, and their status drastically alters. Driven by differing goals, they compete on the battleground of intelligence for their respective camps. With new grudges and old resentments, they grow opposing ideals. Amidst intelligence battles and gunfire, the trio calmly accepts their fates. They find peace in their choices, reconcile with each other, and unravel the enemy's schemes through blood and flesh, unyielding love and ideals. Ultimately, they steadfastly uphold their inner ideals and beliefs.