The Mask is set against the backdrop of the CCP's anti-espionage operations in the early days of the liberation of Harbin. On the first day of the twelfth lunar month in 1948, Li Chunqiu (Zu Feng), a military spy who had been lurking in Harbin for ten years, was suddenly awakened and asked to implement the "Black Tiger Plan". Li Chunqiu's ten years of peaceful life were completely disrupted. He had to make choices about his faith, his family responsibilities, his emotional belonging, and faced extreme circumstances. After a series of thrilling battles of wits and courage, he finally saw the bloody cruelty of the Kuomintang secret service. Inspired by the Communists, he abandoned the dark and joined the light, realizing the transformation of his faith from anxiety to awakening.