A science fiction thriller that depicts all students across the country fighting against unidentified objects ahead of the CSAT and fighting for extra points.

Students in 3rd grade 2nd class at a high school are supposed to study hard for their entrance exams. Instead, they must fight a war against bizarre alien creatures that appear in the sky. Suddenly, strange alien creatures appear over the skies of Earth and cause heavy casualties. To increase the military power in Korea, the government announces that all universities and high schools will organize into reserve forces. Meanwhile, students in 3rd grade 2nd class at the high school become confused by the situation they face. They studied hard for their university entrance exams, but those exams won't be held this year. Instead, they are assigned to the reserve forces. Platoon Leader Lee Choon-Ho (Shin Hyun-Soo) and Sergeant Kim Won-Bin (Lee Soon-Won) come to the high school to train the students. Lee Choon-Ho is strict on the students, but he cares about them a lot. Park Eun-Young (Lim Se-Mi) is the homeroom teacher of 3rd grade 2nd class and places the students' safety first.—AsianWiki