In May, there is not much time left for students preparing for the college entrance examination. The midterm exam has just ended and a new round of rankings has been released. Sisters Jiang Yina (played by Nam Gyu-ri) and Mingxiao (played by Sun Yunen) ranked fifth and fourth respectively, with excellent grades. Jiang Xian, a boy in the same class, likes Yina. Knowing that she likes to listen to music, he gave her an mp3 and invited them to a party on Friday night. The special training for top students will start on Saturday. This is the last joy. It was a pleasant night. On May 24, Saturday, the special training class for top students began. Huimin disappeared. Suddenly, all TVs broadcast the picture of Huimin trapped in a closed fish tank. A voice came through the radio, asking everyone to retake the midterm exam and answer all the questions correctly before the exam can end. If they cannot answer them in time, students will die one by one. The school's communications have been completely cut off, and the teachers who tried to go out of the school for help have also died. The head teacher Huang Changxu (played by Lee Fanxiu) asked the students not to panic. Everyone tried to find the missing students while answering the questions. However, it was not because the answers were overtime or they could not answer them. The students died one after another. Ina deduced that the order of death was based on the midterm exam ranking, and the next person to die was Mingxiao. Ina comforted Mingxiao, who had already panicked, while trying to find the answer. Jiang Xian protected Ina all the way. More and more people died, and the questions were still incredible. Ina deduced through a riddle that this murder case was related to her friend Zhiyuan (played by Yoon Jung-hee) who died two years ago.