S1, E3: Kang Mireu, who's trapped in a punishment room, uses all his strength to escape, but it's of no use. Park Muyeol and Lee Jaegyu use the security camera displays to find Kang Mireu. The students who were looking for their missing teacher enter their teacher's room only to find that there is a letter there are well. Meanwhile, the students who set Kang Mireu free find out that the student their teacher Yun Jong-il was looking for in the student registry last night was a student by the name of Kim Jinsu.