Xue Ying, a top-tier assassin, meets an untimely death and is reborn in the body of Qiao Ying, who has suffered all kinds of bullying. The original Qiao Ying was harshly treated by her mother and younger sister at home, and was labeled a poor student at school. The returned Xue Ying casts off her former weakness, displays astonishing knowledge, and easily solves world-class math problems. While protecting her younger brother Qiao Yi, who has a lame leg, and preparing for exams, she secretly rebuilds her mercenary group, engages in powerful maneuvering with the mysterious great figure Qin Hanyue, conceals her identity as an assassin, and exacts revenge on her former foes.