Oh Jong, a woman in her 30s, is raising three sisters who all have different fathers. She is a barista master who has skills in coffee roasting. She has a bright personality and her dream is to share happiness and tell stories through coffee. One day, she meets a single, company team leader Choi Chang. He believes coffee is like math and roasting has to be done with exact measures. They compete to make the "best coffee." Warm-hearted Oh Jong and stubborn Choi Chang grow in love through coffee. Their relationship reaches a new stage when Oh Jong's past is suddenly revealed.
