Su Jin'er, an illegitimate daughter of the Su family, originally only wanted to enter Prince Jing's residence as a favored concubine. But through an unexpected twist of fate, she caught the eye of Shen Zhao, the heir apparent, and was chosen as his principal wife. After their marriage, she navigates various conflicts within the prince's household while accompanying Shen Zhao in investigating an old case from seven years ago, involving the defeat at Hanguan Pass and the Xie family's conviction. The mysterious Xie Lanyin enters the residence to seek refuge under the guise of a frail, sickly woman. Her peculiar words and actions arouse Su Jin'er's suspicions. Following clues involving scented sachets, old account books, and Qingci Temple, everyone gradually digs deeper into the past and approaches the heart of the mystery. But an unexpected poisoning crisis suddenly erupts, bringing even more mysteries to light. The many truths surrounding Xie Lanyin have yet to be fully revealed.