Meet Seon-ji, a lovely aspiring patissier with a secret that even she herself is unaware of: She is under a curse that transforms her into an unmanageable she-devil every night. Daytime Seon-ji has no recollection of Nighttime Seon-ji and the latter's ungracious behavior. One summer night, Nighttime Seon-ji bumps into their awkward and jobless neighbor Gil-gu in a spectacular fashion. Seizing this opportunity, Seon-ji's family hires Gil-gu to work the night shift of watching over her. While crushing hard on Daytime Seon-ji and navigating his bewildering late night dates with her, Gil-gu determined to unravel the curse and help both versions of the girl find their own futures.