Lee Yeoreum, a university student, unexpectedly reunites with her first love, Ji Suyeong, and his fiancée, Bae Han-gyeong, the owner of the café where she works. Their relationship began in high school when Yeoreum's mother worked as a housekeeper at Suyeong's family home. After years of heartbreak, they meet again, but this time, Suyeong unknowingly drinks a potion that makes him fall in love with Yeoreum. With the potion's effects lasting one year, will their love become real, or will it fade once the potion wears off?