At the end of the Qing Dynasty and the beginning of the Republic of China, the wealthy Lin family was wiped out overnight. Later, Lin Mengchen, the only daughter of the Lin family, was sold to the unjust wealthy Huang family to marry the deceased son of the family. When Mengchen was about to be buried alive, Xiaosheng, the number one killer of the killer organization Blood Sacrifice Hall, happened to receive the task of killing the Huang family and saved Mengchen by mistake. Mengchen witnessed the whole process of Xiaosheng's killing. Not only was she not afraid, but she also regarded Xiaosheng, who was carrying out the task, as a benefactor. Ye Xiaosheng decided to take Lin Mengchen with him, and from then on, brother and sister would protect her in this life. Ten years passed in a blink of an eye. In order to give his "sister" a good growth environment, Xiaosheng has been living in a dual identity. At home and in front of Mengchen, he is the businessman Ye Zhanggui, doing some business for a living. In the dark where Mengchen can't see, he is still the number one killer of the Blood Sacrifice Hall. But what Xiaosheng didn't know was that his innocent sister Mengchen, who he had cared for for ten years, actually found out his details, and secretly joined the Blood Sacrifice Hall and became his female apprentice-the new killer Guyu.