After crashing her ex's wedding, high school teacher Siyeon drowns her heartbreak in a hotel bar, only to end up in a reckless one-night stand with a charming young man. Although she’s ready to forget the night ever happened, she's thrown into chaos when he appears at her school as her new coworker. As if that wasn't bad enough, he turns out to be Hajun, a former student she taught years ago. While Siyeon struggles to keep her walls up, Hajun boldly closes the distance, refusing to let their past—or their night together—stay buried.