**Time Travel**: Modern girl Shen Lan accidentally traveled to Shanxi in 1937, and her soul possessed the female agent of the same name. The time anchor point is set on the eve of the Japanese army's full-scale invasion of China and three months before the Taiyuan Defense War.
- **Spy War System**: The Taiyuan underground intelligence network of the CCP used the teahouse as a cover to set up a secret transportation station. The Japanese military police headquarters uses advanced technologies such as fingerprint recognition to enhance confidentiality, which is in sharp contrast to the agents' native methods of deciphering.
- **Historical Node**: The story will be integrated into real historical events such as the Great Victory of Pingxingguan, the Battle of Taiyuan, and the Hundred Regiments War. The Japanese poison gas experiment in Shanxi and the battle for railway lines will become key plot points.
