Zhang Qiao'er, the legitimate daughter of the Prime Minister's household, is obese and repeatedly faces broken engagements and ridicule. Zhao Yong, a modern fitness enthusiast, unexpectedly travels through time and becomes her bodyguard, determined to help her lose weight and transform herself. During her weight-loss journey, Zhang Qiao'er wavers several times and gives up on herself, while her stepmother, Madam Liu, and her younger half-sister, Zhang Ling'er, continually scheme against her and obstruct her progress. Later, Zhang Qiao'er discovers the truth that her biological mother was poisoned by Madam Liu. Filled with grief and determination, she grits her teeth and perseveres, successfully losing weight and transforming herself while gathering evidence of the crimes. Madam Liu then frames her in another scheme, forcing her into a political marriage far away to a brutal foreign khan. Zhang Qiao'er enters the palace to argue her case and refuses the marriage even at the cost of her life. In the end, she brings the villains down and clears her mother's name. She and Zhao Yong, who has stood by her side throughout, develop feelings for each other and finally become a couple.