In 1944 Harbin, under the puppet Manchukuo regime, Song Zhuowen, an underground party member disguised as a railway patrol officer, is mistakenly recognized by the head of the special service section, Guan Xue, as his life-saving benefactor—actually Zhuowen's long-lost twin brother, Song Zhuowu. Zhuowen, aiming to uncover the ultimate mission of Kwantung Army section chief Asano Daigo's visit to Harbin, devises a plan to use Guan Xue to infiltrate the special service section. However, the sudden appearance of Zhuowu puts Zhuowen in an unexpected predicament. Guan Xue, cold-blooded and suspicious, and Zhuowu, impulsive by nature, often inadvertently sabotages Zhuowen's operations. It's only through the arrangement of their superiors that the two brothers start to cooperate and protect each other. After several tests, avoiding the open and covert struggles among their colleagues in the special service section, they finally earn the trust of Guan Xue and the Japanese officials. Within this short year, the underground party members, after enduring immense hardships, manage to uncover and thwart a secret operation jointly plotted by the Japanese army and the Soviet Union, expose the puppet Manchukuo spies lurking within their party, and welcome the final victory of the war.