Cui Jin, the second daughter of the Cui family, dies from poisoned wine in her past life after being betrayed by her husband, Shen Zhiheng, and her elder sister, Cui Ruyue. Shen Zhiheng, who secretly loved Ruyue, believed Cui Jin had stolen his true love and conspired with Ruyue to ruin her. Upon dying, Cui Jin is reborn to the day before her joint wedding with her sister. Her father, Minister Cui, has prepared two pills: a fertility pill that ensures easy conception but increases marital desires, and a Heart-Union Pill that guarantees lifelong affection but results in sterility. In her previous life, Cui Jin took the Heart-Union Pill for Shen Zhiheng, only to be abandoned when he discovered she had not given him the matching half. Ruyue took the fertility pill for Prince Xin, the Crown Prince candidate, but died in childbirth due to court intrigue.
This time, Cui Jin overhears the arrangement and realizes the traps set for her. She understands that Shen Zhiheng will rise to power with the support of her maternal family, while Prince Xin faces political peril. Deciding to seize her own destiny, she publicly claims the fertility pill and demands to marry Prince Xin instead of her sister. Ruyue, who has also been reborn and knows Shen Zhiheng will become a powerful minister, eagerly agrees to the switch, believing Cui Jin is walking into a doomed marriage with a prince who favors another woman. Cui Jin’s mother, aware of the past life’s tragedies, withdraws financial support from the Shen family, leaving Shen Zhiheng’s wedding modest and embarrassing compared to the Prince’s grand procession.
On her wedding night, Cui Jin confronts Prince Xin, Xiao Lin, about the switched marriage. Instead of denying her scheming, she confesses that she orchestrated the swap out of obsessive love for him, risking execution. Her honesty and beauty disarm him, and he allows her to remain in the manor, though he maintains his devotion to his Secondary Consort, Lin Zhao, a warrior woman from the southern borderlands who shares his past. Cui Jin accepts her position, aiming not for his heart but for the status of Empress.
Tensions rise when Lin Zhao frames Cui Jin for poisoning her using a southern toxin. Cui Jin, anticipating the trap, had secretly swapped the poison with a harmless variant and arranged for the evidence to point back to Lin Zhao’s own schemes. She clears her name and gains the Prince’s reluctant respect, while Lin Zhao’s credibility begins to crack. Meanwhile, Shen Zhiheng and Cui Ruyue’s marriage is marred by his arrogance and her growing realization that his rise is not as guaranteed as she remembered. Cui Jin systematically dismantles their alliances, exposing Shen Zhiheng’s infidelity and Ruyue’s past malice. As political storms gather around Prince Xin’s faction, Cui Jin navigates the treacherous inner court, using her knowledge of future events and her own cunning to secure her position, turning the tables on those who wronged her in her previous life.
