Shy and unpopular Park Dasom rushes to meet her only friend, the beautiful and adored, Chae Iseul. Instead, she finds Iseul's dead body, or rather, its hollow shell. Dasom enters it and takes over Iseul's seemingly perfect life. But as Dasom discovers horrific family secrets, she wonders where her friend went, and if it was an accident she ended up in Iseul's shell.