Wanqing enters Prince Jing's residence as a concubine and a substitute, living like a lone sparrow in a secluded courtyard, neither competing nor vying for favor. Gu Han, a highly skilled commander of the guards, strictly observes the rules, yet as he protects her day and night, he secretly falls in love with her. The two struggle repeatedly between the gulf in their status and the constraints of etiquette. After Su Nianrou, the woman who has always held a special place in his heart, returns to the residence, Wanqing resolves to leave and reclaim her freedom, only to face a series of conspiracies involving the destruction of her reputation and false accusations. Gu Han repeatedly breaks the rules and risks his life to save her. From restrained, unspoken affection, they progress to fighting back side by side, ultimately exposing Su Nianrou's vicious schemes.