Lee Jieun, Bae Suzy and Park Jiyeon were the best of friends. They were an inseparable trio and they attend Jongduk High School, one of the most prestigious high schools in Seoul. Their lives were normal and fun until one day, their world changed a 180 degrees. 3 new students came to their class. They were Yoon Doojoon, Lee Gikwang and Yang Yoseob. They were indifferent and cold to those they hate. But what changed their attitudes was when their music teacher paired them up with the trio: DoojoonxJiyeon, GikwangxSuzy & YoseobxJieun. Slowly, they formed bonds and learned the meaning of love.