Having never been involved in a long-term relationship, Ha-yoon was hoping that her current boyfriend, Nam Tae-ryeon, 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-ryeon are allowed to spend as much time apart as they want, without calling things off completely. Agreeing to her terms, Tae-ryeon and Ha-yoon draw up a contract in which the terms of their grace period are clearly stated. While Tae-ryeon goes about his life, Ha-yoon somehow finds herself signing an entirely different contract with her best friend and college colleague, Kang-jin.