Mu Fengyan, a modern master of ancient martial arts who excels in both medicine and poison, transmigrates into the body of the legitimate daughter of the Prime Minister. When she awakens, she finds herself buried alive inside a coffin. After escaping, she encounters Ye Lijue, the Regent Prince, who has been afflicted with several deadly poisons. She casually gives him medicine and saves his life. Upon returning to the Prime Minister's residence, she punishes her scoundrel father, stepmother, half-sister, and other wicked relatives while protecting her mother, Han, who comes from a wealthy merchant family. Wary of the Regent's power, the Emperor arranges for Mu Fengyan, who bears the destiny of the Phoenix Maiden, to marry him. While using her medical skills to neutralize the poisons in Ye Lijue's body, Mu Fengyan builds her own secret guard force and helps her mother obtain a divorce and leave the Prime Minister's residence. Princes and noble ladies at court scheme against the couple, but she thwarts their plots with her mastery of poison and her intelligence. Ye Lijue, meanwhile, becomes utterly devoted to his wife and stands by her in everything.