The students and teachers at Sungjin High School receive a terrifying shock when they witness the start of an alien invasion. Coming from the skies, horrific “eggs” hatch violent insect-like creatures that attack humans. The invasion is worldwide, and the South Korean military fears it will be overwhelmed. In desperation, the President announces that mandatory conscription will begin – and that all third-year high schoolers – male and female – must join the armed forces. Soldiers arrive at Sungjin High School. And the third-years – who only have 50 days until they are supposed to sit their university entrance exams – must commence their military training in the school playground. They must learn how to shoot rifles, fight hand-to-hand, and navigate obstacle courses...in their school uniform! Putting the students through their paces will be the platoon leader Lee Chun Ho. Meanwhile, the class teacher Park Eun Young is determined to do what she can to keep her students out of harm’s way. Will the high schoolers help save the planet from doom? Adapted from the webtoon "Duty After School" (방과 후 전쟁활동) by Ha Il Kwon (하일권).