In 1935, the Communist Party's underground organization in Shanghai was severely damaged by Kuomintang agents, and the top-secret files were in great danger. Underground Party members Xu Feng and Li Jing were entrusted with a crucial mission. They engaged in a life-and-death struggle with traitors and agents, and faced the hatred of former brothers turning against them. After numerous sacrifices and tests, they finally retrieved the top-secret files and completed their revolutionary mission.