In the autumn of the 26th year of the Republic of China, the Battle of Songhu came to an end. The Chinese army withdrew westward and Shanghai fell. The concession was reduced to an isolated island, and the four forces staged a silent strangulation in this tiny land. The military command, the Central Command, the Chinese Communist Intelligence Organization, Wang Puppet Secret Service Headquarters "No. 76", The Japanese Mei Agency, the British, American and French Concession Patrol Room... Behind every business card, there may be a poison-hardened knife hidden.
In this invisible war, there is a group of people whose names will not be recorded in the annals of history, whose achievements are unknown, and whose sacrifices cannot even be erected with monuments. They live like shadows and are silent like frost, but they are willing to walk on the edge of a knife just for these four words - the mountains and rivers are safe.
