Bo-eun (Moon Geun-young) is an ordinary 15-year-old high school girl who worries about grades and has a crush on her school's baseball team ace, Jung-woo. One day, Bo-eun's grandfather orders her to marry Sang-min (Kim Rae-won) because of a pact he made with Sang-min's grandfather during the Korean War. Despite the grandchildren's opposition, they are forced to marry because of Bo-eun's grandfather's strong influence. However, later on in the story, it is revealed that Sang-min actually loves Bo-eun. Bo-eun's undercover married life begins: She pretends that she doesn't have a husband and starts dating Jung-woo. And her only best friend cannot help but to be envious of Bo-eun as she also has a crush on Jung-woo. But Bo-eun believes that she can manage both men and live a double life. Everything goes smoothly until Sang-min becomes an art teacher at Bo-eun's school and the duo have to try to keep their marriage a secret. From there, their relationship begins to grow. After an incident, Bo-eun's family finds out about Jung-woo. After talking to her mother, Bo-eun finally realizes that she loves Sang-min. At the school festival she breaks up with Jung-woo and confesses her feelings to Sang-min in front of the whole school.