BFFs Yejin and Haeri are in the same class. One day, Yejin finds out Haeri is keeping a shared diary with girls from another class. For Yejin, being a bestie means being the 'only one.' She becomes restless and nervous: 'Is Haeri closer to those kids than me?' 'Are they talking about me on those pages?' On the verge of losing her best friend and her secrets all at once, Yejin tries to grow out of an era where one friend was her whole world. (LEE Ranhee) (LEE Ranhee)