On the eve of the dreaded university entrance examinations, the lives of 24 of the smartest and brightest students at one high school, are on the line. Locked inside a classroom and nowhere to escape, a television monitor broadcasts a terrified Hae-yeong, the top student at the high school, tied up and seated on a chair inside an aquarium that slowly begins to fill with water. A voice from the monitor announces if the 24 cannot finish the exam administered within the allotted time given, Hae-yeong will die and so will everyone held captive inside the classroom. Thus begins the examination that will determine whether they live or die.
At the same time as murder suspect Yeo-hoon is brought unconscious to the emergency room following a shooting incident, an assailant breaks into the house of Tae-jun, the emergency room’s doctor in charge, and kidnaps his wife. The kidnapper calls the doctor and tells him to bring Yeo-hoon to him. To retrieve his wife, Tae-jun has no option but to save the patient and sneak him away before the police can notice.