Set in a period where society does not allow females to be educated nor employed, Kim Yoon-hee (Park Min-young) disguises herself as her brother, Kim Yoon-shik, in order to make ends meet for her family. She goes through a series of odd jobs, mainly at a local bookstore, before she gets offered a chance to increase her earnings by becoming a substitute test-taker (an illegal act) for the upcoming entrance examination in the prestigious Sungkyunkwan.

She gets caught by the upright Lee Sun-joon (Park Yuchun), who later acknowledges Yoon-hee's talents, and even encourages her to enroll in the university. There, she must bear with the endless mischief of upperclassman Gu Yong-ha (Song Joong-ki), put up with the constant mood swings of roommate, Moon Jae-shin (Yoo Ah-in), avoid getting in trouble with the strict, student body president, Ha I-soo (Jun Tae-soo), keep her secret from being discovered, all the while trying to maintain her growing affections for Lee Su-joon, at bay.