In 1940s Shanghai, struggling actor Ding Yi is forced to impersonate a blind cryptography expert after agent Gu Yinshan mistakenly kills the real man. Disguised as his assistant, Gu Yinshan joins Ding Yi to infiltrate Japanese intelligence with the help of theater owner Xian Biyun. Facing constant danger, the unlikely duo form a deep brotherhood, but their clashing loyalties lead to an inevitable test of trust and sacrifice.