Song Qingci, the Song family's biological daughter, was taken in by her master, Shen Wenshan, when she was young. Under his guidance, she mastered both medicine and poison. When Shen Wenshan learns that Song Qingci is returning to the Song family, he secretly writes to the Pei family, asking them to look after his stubborn, ungrateful disciple. After returning, Song Qingci is coldly treated by her father, Song Zhiyuan, ostracized by the adopted heiress, Song Zhirou, and betrayed by her fiancé, Zhao Shijie. At her engagement banquet, she publicly exposes Zhao Shijie and Song Zhirou's affair and cuts ties with the Song family. As she leaves, she unexpectedly saves Pei Yanzhi, the Pei family's heir, who has been poisoned by a rare toxin. Recognizing her as the person entrusted to him in the letter, Pei Yanzhi strikes a deal with her: a marriage lasting one year.