In an all-female high school in South Korea, the Jookran High School for Girls, teacher Mrs. Park, nicknamed "Old Fox" due to her sadistic method of teaching, circles several points in the students' yearbooks and calls her former student turned new fellow teacher, Hur Eun-young, that "Jin-ju, is definitely dead, but still attending school". Moments later, she is strangled with a noose by an unknown figure, her body later discovered the next day by three new senior students: the talented artist but superstitious Lim Ji-oh; the timid outsider, Yoon Jae-yi; and the weird, sullen, and deeply unpopular Kim Jung-sook. Ji-oh and Jae-yi arrive early as they are the new class monitors, while Jung-sook has always been a die-hard. Their form teacher position is now held by Mr. Oh, nicknamed "Mad Dog", who likes to give corporal punishments to his students, in particular Ji-oh due to her superstitions, as well as harassing and overly praising the class' top scorer, Park So-young.