Jiang Leyao suffers a horrific assault by a man in a mouse mask and is subsequently blamed by the Ning family for having an affair. Betrayed by her maid, Rong’er, Jiang Leyao is brutally beaten by the Ning family and thrown into a woodshed, which Rong’er sets on fire. In the blaze, Jiang Leyao unexpectedly rebirths back to a month earlier, on her 15th birthday. Desperate to save her family, she rushes to her village, only to find that Rong’er has already burned it down, killing her parents. Discovering that Rong’er has stolen her mother's jade pendant to impersonate her and marry into the Ning family, Jiang Leyao confronts and slaps Rong’er at the Ning estate, vowing revenge.

Xiao Jingchu, leader of the Xuanyin Bureau, is investigating a gambling house case that leads to Rong’er. To find her parents' killer, Jiang Leyao pretends to be Rong’er's maid to enter the Ning family. When Xiao Jingchu arrives to arrest Rong’er, Jiang Leyao stops him to keep her source of clues alive, even grabbing his blade with her bare hands. Xiao Jingchu confiscates a meaningful hairpin given by Jiang Leyao's late mother and demands she come to the Xuanyin Bureau for interrogation that night if she wants it back. For her revenge, she bravely accepts the dangerous invitation.

Jiang Leyao goes to the Xuanyin Bureau, where Xiao Jingchu interrogates her. After a tense confrontation and proving her innocence regarding the gambling house, Jiang Leyao proposes an alliance: she will spy on the Ning family for him in exchange for her hairpin and survival. Back at the Ning estate, Rong’er frames Jiang Leyao for stealing a gold hairpin, leading the Ning family to torture her by crushing her fingers. Just as she is suffering, Xiao Jingchu arrives at the Ning estate under the pretext of chasing an escaped suspect, bringing her a glimmer of hope.

Xiao Jingchu rescues Jiang Leyao from her torturers and retaliates against Rong’er. Jiang Leyao exposes the Ning family's corruption and officially agrees to be Xiao Jingchu's inside spy to find the illegal gambling house's ledger in Lord Ning's study. Meanwhile, Rong’er faces severe punishment from her rivals within the household. Seizing the opportunity for psychological revenge, Jiang Leyao returns and deceitfully advises Rong’er to use an aphrodisiac to seduce Ning Tao.

Rong’er gains procurement power in the Ning family, and Jiang Leyao suggests a celebration banquet to create a distraction. To find the secret ledger, Jiang Leyao bribes staff and allies with a domestic abuse victim, Mother Zhao, discovering that Lord Ning's study likely contains a hidden chamber. Rong’er tries to sabotage her by having Ning Tao corner her, but Jiang Leyao cleverly escapes to meet Xiao Jingchu, who becomes furious upon learning of Ning Tao's harassment.

Jiang Leyao uses clues about an illegal gambling den run by a servant's son to manipulate Rong’er into targeting a rival, Qi Zhen. At a grand banquet, Jiang Leyao successfully exposes Qi Zhen, leading to her punishment by Lord Ning. During the event, Rong’er's gambling-addicted biological father, Chang Shu, appears. Jiang Leyao temporarily covers for Rong’er to prolong her suffering, but she soon discovers that Ning Bingqing is secretly collaborating with Rong’er.

Jiang Leyao and Xiao Jingchu manipulate Rong’er’s father into trapping Rong’er in a gambling debt. Later, Jiang Leyao discovers Rong’er serves poisoned pastries to Ning Tao. Instead of stopping it, Jiang Leyao lets him die to exploit the situation. When Rong’er tries to frame her, Jiang Leyao exposes Rong’er’s identity fraud. Infuriated, Lord Ning sentences Rong’er to death, but Jiang Leyao intervenes, asking to keep Rong’er as her personal maid to continue torturing her. She also confirms Ning Bingqing is the mastermind behind Rong’er.

Jiang Leyao hands the ledger to Xiao Jingchu. Ning Bingqing treats Jiang Leyao with hostility and orders Rong’er to drug Jiang Leyao's soup. Knowing the trap, Jiang Leyao plays along to uncover the truth about her past nightmare. Ning Bingqing takes her toward Haitang Xue, but Xiao Jingchu pursues them and rescues an unconscious Jiang Leyao, who has been poisoned with Furong powder. In her coma, her horrific memories of the original assault resurface.