In 1937, the smoke of the Battle of Shanghai had not yet dissipated, and Shanghai became an "isolated island". This book takes the undercover journey of Li Ji, a special agent of the Military Intelligence Department, as the main line, revealing the cruel truth of the spy war in Shanghai during the Anti-Japanese War. From the secret operations of the "Beauty Snake" group of the Military Intelligence Bureau to the thrilling steps of the Japanese Military Police Headquarters, the story combines real historical events with fictional spy war plots to show the struggles and choices of small people in troubled times. When Li Ji disguised himself and infiltrated the Japanese military spy class, when the cheongsam woman Wu Yukun dealt with various forces, and when the good news bird Yu Moqing wandered between seduction and intelligence, the intelligence network they wove with flesh and blood became a sharp blade that pierced the darkness.