Su Qing, an underground member of the Communist Party of China, alias "Secretary Shen" lurks in the Japanese spy agency in Peiping and is responsible for collecting intelligence. She met the unidentified "businessman" Lu Zheyuan. The two were forced to cooperate on a mission and found that they were both anti-Japanese (Lu Zheyuan was a military agent). They teamed up to pass on Japanese "mopping up" information, but faced a crisis of identity exposure.
