During the peaceful period of Song and Liao, Tang Ziyan, an agent originally trained by the secret organization "Phoenix Fire Army," is placed in the Imperial City Department in Beijing. While Tang Ziyan wanted to quietly quit and have a peaceful remainder of her life with her husband Zhou Qian, her husband was taken away by the Phoenix Fire Army to threaten Tang Ziyan. She now has a new mission set by the army: To assassinate the visiting envoy of the Northern Dynasty. During this period, Zhou Qian'an was shot and killed by the Phoenix Fire Army and Tang Ziyan is determined to take down the Phoenix Fire Army. She pretended to not be wavered and continued to plan the next step of the assassination plan, but is surprised to find that the target is just by her side. In the end, Tang Ziyan along with the envoy work together to defeat the Phoenix Fire Army, quelling a scourge and returning peace to Beijing.