In the winter of 1947, in order to seize the distribution map of tens of thousands of advance troops in Jiuling, Northeast China from the bandits, the captain of the 203rd squad of the Northeast Democratic Alliance Army, Shao Jianbo (played by Lin Gengxin), appointed investigator Yang Zirong (played by Zhang Hanyu) to go undercover and sneak into the largest bandit mountain "Weihu Mountain". Yang Zirong won the appreciation of the bandit leader Zuoshan Diao (played by Liang Jiahui) and the eight kings under his seat by virtue of his wit and response, and was named "Old Nine" of Weihu Mountain. Zuoshan Diao was born suspicious and sent people to test Yang Zirong many times. Yang Zirong dealt with the bandits in many ways while passing on intelligence for his comrades down the mountain. One wave has not yet settled, and another wave has risen. Luan Ping (played by Du Yiheng), the bandit liaison adjutant who was captured alive by the 203rd squad, escaped in the chaos. Knowing the details of Yang Zirong's undercover, he appeared in Weihu Village and confronted Yang Zirong face to face. Yang Zirong was attacked from all sides and fell into a comprehensive crisis...