In the autumn of 1937, the smoke of the Battle of Songhu still lingered. The Shanghai Concession became an "isolated island" with undercurrents surging. Mechanical engineer Shen Qingyuan returned from Nanyang and wanted to serve the country with technology, but was forced to get involved in a secret espionage war between various forces. He must use gears, radio waves and lies to protect a secret passage to the rear in the multiple cracks between the Japanese invaders, No. 76, Military commanders, underground parties and concession patrols.
