In the winter of 1937, Nanjing fell, and the military's ace killer Xu Yaoran was ordered to lurk behind enemy lines, codenamed "Hidden Gun." He wanted to liquidate traitors and hunt down high-ranking officials in the heart of the Japanese and puppets, but he didn't know that his most trusted contact, the cold-as-moon Shen Keqing, had already laid a fatal trap for him. When guns are pointed at each other, is it national hatred or personal hatred that is being settled?
