In A.D. 690, Empress Wu Zhechen changed the name of the Tang dynasty to the main one and made Luoyang the capital. After receiving information that the Stone Palace is secretly restoring the 'Phoenix Heavenly Flower', an ancient Persian absolute weapon, Mujeokcheon immediately convenes the Black Army and issues a secret order to bring the weapon blueprint. Three years later, when lightning strikes from the sky, turning the Nanseong area of ​​Joju into ashes, Mu Zhuqian summons the Black Widow's President, Mu Yeon-woo, to investigate the incident thoroughly. Mu Yeon-woo discovers something strange while investigating the case and sends burnt remains to Tongcheongak to ask for an autopsy. When the fire and lightning incident is finally revealed to be the work of a person, not a natural disaster, Yeon-woo Mu goes to meet the largest merchant in Yeongju, 'Gokpilaksa', to catch the real culprit...