On the eve of the victory of the Anti Japanese War, Ou Xiao'an, an underground party member of the Communist Party of China lurking in the military statistics department, escaped from the prison of the Japanese Biochemical Poison Gas Research Institute. He was seriously injured and unconscious on the way, and was found and rescued by the Chinese Expeditionary Force. After waking up, Ou Xiao'an found that he had lost his memories of nearly four years in prison. Starting from the endpoint of memories from four years ago, Ou Xiao'an collects scattered memories, secretly investigates, and intends to expose the evil face of Japanese spy Li Shaotang. During this period, he and underground member of the Communist Party of China, Qin Moqing, went from questioning and probing each other to working together, and found the Japanese Biochemical and Toxic Gas Research Institute, capturing the Japanese intelligence commander, Ohashi Kazuno. Ou Xiao'an learned of this intelligence and foiled the malicious plan, while exposing the true face of Li Shaotang, a Japanese spy. Ou Xiao'an, code-named "Lonely Star" within the underground Communist Party, finally returned to the embrace of the party organization.