Irene was lonely when she moved into a completely new town and apartment with her mother. But her lonliness was soon gone when she met the new tenant and her next door neighbour, Seulgi and they became best of friends within a short time. Irene was very fond of Seulgi but sometimes she found her weird, especially, Seulgi being so overprotective and obsessive of her and their friendship, irritated he sometimes. Soon after getting into a high school, Irene made new friends and eventually started avoiding Seulgi on purpose, thinking that ending their friendship would keep Seulgi away from her and her new friends and gradually they lost touch with each other. But soon after that Irene's friends started getting murdered one by one in a mysterious way and Irene suspected it was none other Seulgi and decides to stop her. Can Irene find Seulgi before all of her friends are dead and stop her death list? Or she shares the same fate as her friends? Is it really Seulgi who is murdering her friends?