Known as a bully caretaker, "S" seeks retribution for her clients who have been bullied, provided they pay her fee.
Despite her reputation, "S" is actually a studious person named Kang Song Ih, who adores her twin brother Kang Ah Eul above all else. Ah Eul is a student at the prestigious and costly Chungha High School, but during the winter holidays, he tries to end his own life. In an attempt to uncover the reasons that caused her brother's suicide attempt, Song Ih decides to masquerade as Ah Eul and enrol in Chungha High School. While there, she discovers the events that led up to Ah Eul's actions, which include the involvement of the intriguing yet dangerous Suh Ga Yoon.
