Shen Yunli, the orphaned daughter of the Marquis of Dingbei, has her inheritance seized by her aunt and is forced to marry in place of another bride to the gravely ill heir apparent. The plum-blossom hairpin she hands over is merely a decoy; the true black-gold key is hidden on her person. After entering the Duke of Anguo's household, Shen Yunli uses her exceptional medical skills to treat Pei Yan, the heir apparent. Together, they gradually uncover the old case in which her father was wrongly accused and expose the evildoers behind it. From turmoil within the household to clearing her family's name in court, they stand side by side to restore the honor of their fathers and protect their families' peace.