In the "July 15" counter-revolutionary coup in 1927, in order to rescue the Communist Party member Ren Zhiyuan, Xia Hengxuan died generously, leaving his sister Xia Yuzhu and the maid Shuangju to depend on each other. The weak Yuzhu made a living on her own, while Shuangju joined the Kuomintang spy organization under the introduction of Hengxuan's lover Xiao Chengbi. A few years later, Yuzhu accidentally rescued Ren Zhiyuan. After Zhiyuan's death, Yuzhu was inspired to become a member of the CCP's underground affairs staff, while Shuangju was reused and promoted in the spy organization. When the Anti-Japanese War broke out, Yuzhu and Shuangju met again, but they were tit-for-tat for their respective missions. Yuzhu discovered that Xiao Chengbi's younger brother Xiao Junhao and himself had a common mission, and the two knew each other and fell in love in battle. In 1949, the Kuomintang fled to Taiwan, and Yuzhu resolutely went to Taiwan to perform the mission, and was discovered by Shuangju, an officer of the Security Bureau. For the sake of faith, Yuzhu died calmly in front of Shuangju, and Shuangju was shocked. On the eve of victory, Yuzhu wrote a magnificent song of faith with her life.