Ten years ago, in a ruined temple in Qingzhou, an assassination changed everyone's destiny. Su Wanning once risked her life to save the heavily injured and feverish crown prince, but her legitimate sister Su Jinyao snatched the silver fish tally and impersonated the crown prince's savior. Ten years later, Su Jinyao entered the Eastern Palace and received pampering, while Su Wanning was forced into a substitute marriage with the cold and powerful official Xie Wuyuan. The two signed a contract marriage for a one-year term, teaming up to investigate the Qingzhou crown prince assassination case and the mystery of Gu Jingyu's drowning. As their mother's last will, half a secret decree, and old account books gradually surfaced, they discovered that the truth of that year implicated the Su Mansion, the Song Family Firm, the Prince Jing Mansion, and even involved plotting against the crown prince and embezzlement.