Su Xianling is an assassin with superb skills but has never really practiced. Aiming to become the world's number one assassin, she decides to take the initiative. In the process of protecting her fellow disciples, she is entrusted with an important task and takes over an unfinished order, but she almost kills Dongfang Jing by mistake. Dongfang Jing is the city lord, but there are murderous intentions hidden in his mansion. Even his mother is eyeing him covetously, so he has to pretend to be incompetent to protect himself. The insurance policy he issued for himself was mistaken by Su Xianling as a kill order, and he almost lost his life. Dongfang Jing, who is scheming, took the opportunity to use Su Xianling's identity as a cover to find the elite troops left by the previous emperor to resist the hostile forces of the empress dowager. But it accidentally uncovered a long-forgotten history. From killing to protecting, a female assassin with superb martial arts but simple and reckless, and the city lord full of pain and hatred, accidentally sparked love...