"Little Black Dress" depicts the friendships, jealousies, hopes and failures of four 24-year-old girls. The girls first met as first year students in college. They seem to be enjoying their 20's, but inside they all have worries. Yoo-Min (Yoon Eun-Hye) still doesn't know what she wants to do. Somehow she gets a job as an assistant to a top writer. Yoo-Min wasn't even sure if she would take the job as an assistant, but after seeing an expensive black mini dress at luxury department store she buys the dress with the writer's credit card and in the process accepts the job. Yoo-Min's job turns out to be more of a babysitter for the writer's twin sons. By chance, Yoo-Min runs into high-school acquaintance Young-Mi who also works as a writer's assistant. Hye-Ji (Park Han-Byul) is busy playing around and living the life of a socialite. One day, she is scouted by a talent agency. She then becomes the face for a high profile ad campaign and shoots to stardom. Her other 3 friends become jealous of her. Soo-Jin (Cha Ye-Ryeon) holds the most jealousy over Hye-Ji's sudden fame, because she has tried unsuccessfully to become an actress. Soo-Jin has failed many different auditions. Compounding her problems, her father's business has gone bankrupt. Min-Hee (Yoo In-Na) has rich parents, but her parents got divorced. Min-Hee now wants to study abroad, but her poor English skills holds her back.
Kim Yeon Woo is an orthopedic doctor who takes up a new post at Taereung National Village, the training center for national Olympic athletes, after she is fired from her previous job. She becomes romantically involved with Park Ji Heon, a young judo athlete, and Lee Do Wook, the short-tempered, crippled director of the facility who is still haunted by the injury that had cut short his speed-skating career. This is further complicated by the presence of the swimming coach, Hee Young, who becomes her rival for the attentions of Do Wook.
Based on the Internet novel of the same and written by Yeo-ni Gui, “Do Re Mi Fa So La Ti Do” is a touching love story with bittersweet elements. Jung-won wears a funny dragon suit, while working at the amusement park, and pours soda on Eun-kyoo, because of his taunts.A short while later, Jung-won finds out that Eun-kyoo has moved into the house next to hers. Eun-kyoo now threatens to tell Jung-won’s parents that she works part time at the amusement park. To keep Eun-kyoo quiet, Jung-won agrees to carry his guitar for a week. Jung-won then starts developings feelings for Eun-kyoo, who is the lead singer in a band called Do Re Mi Fa So La Ti Do. Eun-kyoo also starts to develop similar feelings for Jung-won. The two soon become a couple.With an odd twist of fate, Jung-won goes to the bands rehearsal room and meets a familiar person from her past, a boy named Hui-won. Their relationship makes everything make more complicated. 10 years ago, Jung-won and Hui-won were close friends, but because of a personal matter stopped talking to each other completely. Jung-won is now surprised to learn that her ex-close friend is now best friends with her boyfriend. Will their relationships survive?