Cha Mi-rae is a doctor and single mother to her young daughter Sa-rang. When she gets diagnosed with terminal cancer and told she has one year left to live, she seeks out her ex-boyfriend Han Yeol, a former baseball player. Mi-rae and Yeol were a couple a decade ago, but she broke up with him to study abroad and because she didn't think much of his prospects. Soon after, a serious injury forced him to retire from the sport, and Yeol became the rehabilitation coach of a major league baseball team. Mi-rae is determined to transform still-single, grungy, irritable Yeol into the best father possible for her daughter.