Kang Baek-ho and Ham Yi-seul have been best friends since elementary school. Baek-ho has never acknowledged his attraction to her, unaware that Yi-seul has been in love with him for more than 20 years. Finally, at the wedding ceremony where Yi-seul is about to marry another man, Baek-ho regrets that he never confessed his love for the bride. A mysterious conductor suddenly appears and offers him a second chance to win Yi-seul's heart. Baek-ho travels back in time to various events of their lives hoping to change the outcome of their relationship. But changing the future is not as easy as it seems.