In 1944, in Harbin under the rule of the puppet Manchukuo, Song Zhuowen (Qin Hao), an underground party member disguised as a railway patrolman, was mistaken by Guan Xue (Yang Mi), the chief of the secret service department, as his savior - in fact, it was Zhuowen's long-lost twin brother Song Zhuowu (Qin Hao). In order to find out the highest mission of Asano Daigo, the chief of the Kwantung Army, to come to Harbin, Zhuowen used Guan Xue to enter the secret service department, but Song Zhuowu suddenly appeared, putting Zhuowen in an unexpected predicament. Guan Xue was cold-blooded, suspicious, cruel, and impulsive by nature, and often inadvertently destroyed Zhuowen's actions. Under the arrangement of the superiors, the two brothers cooperated with each other and covered each other. After several attempts, they avoided the open and secret struggles of their colleagues in the secret service department and finally gained the trust of Guan Xue and Japanese senior officials. In just one year, the underground party members went through untold hardships to find out and prevent the secret actions of the Japanese army and the Soviet Union, and uncovered the puppet Manchukuo spies lurking in our party, ushering in the final victory of the war.