Flower girl Su Xiaowan accidentally made a "brother-sister contract" with Gu Yanxi, the eldest son of the jewelry family Gu Mansion, and thus transformed herself into Gu Yanxi's sister and the eldest daughter of the Gu family - Gu Wan'er. However, the story of a sparrow turning into a phoenix is not as beautiful as Su Xiaowan imagined. Facing this poisonous and black-bellied young master, Xiaowan can only respond to his moves and fight with wits and courage. On the way, she also encountered difficulties from the black-bellied young master's maid fan club and the mistress of the Gu Mansion, Mrs. Ru. Although the journey was difficult, fortunately, there was the warm-hearted second young master Gu Ziqian who always accompanied Xiaowan and gave her meticulous care, but the second young master's care for Xiaowan did not seem so simple. What's worse is that in getting along with the two young masters, Xiaowan found herself getting deeper and deeper, and actually fell in love with the most annoying young master Gu Yanxi...