In Shanghai in 1941, military cipher officer Shen Qing disguised himself as an employee of a foreign bank and lurked under Wang Puppet's "No. 76", Responsible for delivering intelligence on the Japanese army's "Purple Lightning Project". She cooperated with the underground party liaison officer "Old Gun", only to find out that "Old Gun" was a Japanese spy. At the critical moment, Wang's pseudo-section chief Gu Yan, who had been monitoring her, came to the rescue - he turned out to be the "rock" of the military command who was hiding deeper, and the two teamed up to crack the "Purple Lightning Project".
