On a Saturday, 170 days before college entrance exam, a special class for 20 top students is held at school. The 20 intelligent students include the loyal high school girl Inah, the bad-boy hunk KANG-Hyun, Ina’s best fernery Myung-Hyo, the top-of-school paranoiac Hye-Young, the hallucination schizophrenic Jo-Beom, the second top insomniac Dong-Hyuk, the timid third top student Jae-Wook, and the over sensitive sixth top student Su-Jin. The only other people left in school together with the 20 students are: the popular teacher Chang-wook, the new English teacher So-young, and the student manager Chi-young. But in the middle of class, “for Elise” rings from the speaker and the TV in classroom shows the top student Hye-young trapped in the water rising tank, screaming and struggling to breathe. And an unidentified voice asks the answer to a mid-term exam question that will cost Hye-young’s life. Nowhere to run, and only 20 students and 3 teachers are in school. The bloody exams start once again for them.