It tells the fateful reunion of twin sisters Cheng Ruo Yun and Chou Yan Zhi as they become involved in political affairs upon encountering the young emperor Li Yan.

The eunuchs have gained control of the palace during the reign of Emperor Wen Zong of Tang. Hoping to free the nation from their clutches, Emperor Wenzhong secretly plots to assassinate the head eunuch Chou Shi Liang, but their plan ends in utter defeat.

Prime minister Wang Ya's entire household is sentenced to death except for his granddaughter twins who barely escape death. The younger sister who is adopted by the Ziyi Bureau assumes the name Yu Bing Er. Determined to take revenge, the older sister changes her name to Yan Zhi and becomes Chou Shi Liang's goddaughter.

Seven years later, emperor Li Yan (Cheng Yi) ascends to the throne. Li Yan resorts to using the Ziyi Bureau to fight against Chou Shi Liang. As a result, the two sisters meet again as enemies unable to recognize their relation by blood.

Adapted from the novel Jian Qi Xing (剑器行) by Zi Fei Hua.