Having never been involved in a long-term relationship, Ha Yoon was hoping that her current boyfriend, Nam Tae Ryun, would be the one to change all of that. But when he announces he wants to break up with her before they even reach their 100th day, Ha Yoon refuses to accept her fate without a fight.
Determined to make this relationship last, Ha Yoon suggests a month-long “break-up grace period” in which she and Tae Ryun are allowed to spend as much time apart as they want, without calling things off completely. Agreeing to her terms, Tae Ryun and Ha Yoon draw up a contract in which the terms of their grace period are clearly stated. While Tae Ryuun goes about his life, Ha Yoon somehow finds herself signing an entirely different contract with her best friend and college colleague, Kang Jin.
Though certain his month away from Ha Yoon would be easy, Tae Ryun begins to have second doubts when he realizes she’s been spending time with Kang Jin. With unexpected feelings of jealousy stirring, will Tae Ryun be willing to let Ha Yoon go without a fight?