Park Da-som is a timid high school girl weighed down by bullying and insecurities about her appearance. One day, she discovers the “shell” of the perfect girl, Cha I-seul—someone she’s always admired—and enters it as if under a spell. Although Da-som is briefly enthralled by I-seul’s dazzling life, she soon comes face-to-face with the horrifying truth lurking in that household. Where is I-seul, and what exactly is this “shell”?