Jiu Yue is a modern woman who dies in a car accident and is immediately recruited by a mechanical entity known as the Rescue Program. The System informs her that her soul has been transferred into the body of an assassin in a fictional ancient world, a character who failed a critical mission and died from a stab wound to the heart. To earn a reward of ten billion cash and return to her original world, Jiu Yue must complete the deceased assassin's unfinished task. Initially resistant to the cliché transmigration scenario, she quickly changes her tune when the financial incentive is revealed, accepting her new identity as a professional killer despite having no prior experience or memory of the character's past.
Upon waking in a forest, Jiu Yue discovers that her body moves with instinctive martial arts proficiency, and violent deaths are perceived as pixelated mosaics rather than gruesome scenes. After surviving an initial ambush by Death Warriors, she spends two weeks navigating the wilderness before making her way to the capital. Along the route, she encounters various assassins sent to kill her, dispatching them with ease while relying on the fragmented skills and knowledge embedded in her new body. Upon arriving in the capital, she is recognized by a man named Nan Xun, who reveals that the original Jiu Yue was a notorious figure in the martial world who had offended a powerful noble, Prince Ping. The original assassin had been hunted down and killed, but due to the System's intervention, Jiu Yue has taken her place.
Seeking protection and information, Jiu Yue follows Nan Xun's advice to approach Regent Prince Sima Qing, the most powerful figure in the capital and a rival of Prince Ping. She presents herself at the Regent Manor, claiming to be an assassin seeking employment. Sima Qing, who has been feigning illness and physical disability to avoid political intrigue, tests her loyalty by assigning her a seemingly impossible task: eliminate a dog within the imperial palace. Jiu Yue interprets the command literally and infiltrates the palace, where she accidentally rescues a neglected palace maid named Xue Er. She kills a vicious dog in the Cold Palace and leaves a message written in dog blood, inadvertently causing a political scandal that implicates Sima Qing in the Emperor's eyes.
Despite the chaos she causes, Sima Qing is intrigued by Jiu Yue's unconventional methods and combat skills. He allows her to stay at the manor, assigning her to work alongside his subordinates, Mo Jin and Fu Yu. Jiu Yue negotiates a high salary of one hundred taels of gold per month, establishing herself as a valuable asset. Throughout her time at the manor, she continues to misunderstand social cues and political subtleties, often causing unintentional offense or confusion. Sima Qing remains suspicious of her true motives, wondering if she is a spy sent by Prince Ping or an assassin with a hidden agenda. Meanwhile, Jiu Yue searches for clues about her original mission, unaware that the System has gone silent, leaving her to navigate the dangerous political landscape of the ancient world on her own.
