The Jang family owns the Hwangso Soy Sauce Factory, which has been making soy sauce for two centuries. When the patriarch's son dies in a train crash, Jang Ha-na, the family's fourth daughter, is chosen to be its next successor. However, because of the tradition of passing the ownership of the company only to a male heir, Ha-na is raised as a boy and must disguise herself as the family son called "Jang Eun-sung" in order to inherit and prevent the factory from being taken over by her mother's scheming rival and her two children as well as a rival competitor.
