At the end of the Qing Dynasty and the beginning of the Republic of China, the Lin family, a wealthy businessman, was wiped out overnight. Later, Lin Mengchen, the only daughter of the Lin family, was sold to the Huang family of the unjust wealthy businessman to marry his deceased son in secret. When Mengchen was about to be buried alive, the killer organized the number one killer of the Blood Sacrifice Hall, Xiaosheng., just received the mission to kill the Huang family, and accidentally saved Mengchen.

Mengchen witnessed the entire process of Xiaosheng's murder. Not only was he not afraid, but he regarded Xiaosheng who was performing the task as a benefactor. Ye Xiaosheng decided to take Lin Mengchen with him. From then on, the brother and sister agreed to protect her throughout their lives.Ten years later, Xiaosheng has been living in a dual identity in order to provide his “sister” with a good growing environment. At home, in front of Mengchen, he is the businessman Ye Shopkeeper, doing some foreign business to make a living.

In the darkness that Mengchen can't see, he is still the number one killer of the Blood Sacrifice Hall.But what Xiaosheng didn't know was that the innocent and innocent sister Mengchen, who he had cared for for ten years, had found out his true identity, secretly joined the Blood Sacrifice Hall, and became his female apprentice - the new killer Gu Yu.