Boeun (Moon Geun-yeong) is an ordinary high school girl who worries about SAT's and has a crush on her school's baseball team ace, named Jungwoo. One day, Boeun's grandfather orders her to marry Sangmin (Kim Rae-won).When they were very young, Boeun's and Sangmin's grandfathers had promised that they would become in-laws. Despite their opposition, they are forced to marry because of the strong influence of Boeun's grandfather. Despite Boeun's undercover married life, she pretends that she doesn't have a husband and starts dating Jungwoo. Boeun believes that she can manage both men and live a double life. Everything goes smoothly until Sangmin starts working at Boeun's school as a student teacher.