Cha Ji-heon (Ji Sung) is an incredibly immature young man who is useless at his job as a director at DN Group, where the chairman is his father (Park Yeong-gyu). Ji-heon has a longstanding rivalry in work and love with cousin Cha Mu-won (Kim Jae-joong), as Mu-won is a mature, hardworking, and seemingly perfect executive, and the two both have a romantic history with Seo Na-yoon (Wang Ji-hye). Spunky and tough Noh Eun-seol (Choi Kang-hee) is struggling to find full-time work because of her juvenile delinquent record and poor academic background. After giving the hiring directors a piece of her mind during a job interview at DN Group, she is surprised to find herself hired by Mu-won (who was captivated by her interview) to be the secretary to Ji-heon. Determined not to be fired from her first professional job, Eun-seol works diligently at putting up with Ji-heon's childishness and keeping him in check. As their working relationship progresses, they earn each other's trust and friendship, and Eun-seol helps Ji-heon deal with his phobias and prove himself capable of becoming DN Group's successor. Things get more complicated when Ji-heon and Mu-won both fall for Eun-seol, who doesn't want to get mixed up with either of them... or does she?