Into the Fire Oh Jang-beom who is one of the South Korean student, is fighting in the Yeongdeok, North Gyeongsang Province battle during the Second World War. When the city is surrounded by the 766th Unit, 5th Division, Korean People’s Army and he is taken into a group consisting of South Korean soldiers led by Lieutenant Kim Jun-Seop attempting escape. The group is eventually reduced to Lt. Kim, Jang-Beom. A North Korean shoots and bayonets the lieutenant. Jang-beom becomes overwhelmed by terror and inexperience and is unable to save him. They are spotted by South Koreans and managed to get on one of the last truck from the town to a hospital Pohang. In the hospital the Lt. Kim is pronounced dead and a smug Jang-beom is seated beside him. Into the Fire HD
Capt. Kang orders Jang-beom to lead a newly-raised student-soldier unit, as Jang-beom is among only three volunteers who have combat prior experience. Three young criminals who are led by Ku Kapjo, are part of the unit , and destroy students’ food items. Then, while they are on conduct their patrol, they are sprayed and are snatched by a KPA sniper. The students suffer heavy casualties before engaging in a retreat. The students’ morale is destroyed by the traumatic incident. Students call Capt. Kang for aid, but the forces of regular soldiers are imprisoned at the Nakdong River. Kang asks his superiors to aid students, but they refuse to divert resources from the vital Pusan front. They dohowever let Kang to leave, and he arranges for vehicles and a small force of South Korean soldiers to relieve the school.
One of the soldiers, Dal-Young, is captured by the 766th Unit and is interrogated by Major Park Mu-Rang. Mu-Rang feels sorry for the student and orders his return to the school, and then goes there himself to evaluate the students’ capabilities. There, he tells Jang-Beom that he and his men will in two hours, capture the school and offer to spare the defenders their lives if they wave a white flag. Kap-Jo beats Dal Young and fights Jang-beom before deserting along with a companion, Chang-wu to escape the Pusan Perimeter. After leaving, the two meet a North Korean truck filled with weapons and other supplies, which is stuck in a road.
The remaining students prepare to defend their school, by raising the flag, not white but the South Korean national flag and Major Park is making his own preparations to prepare for the assault. The assault begins and the students could cause serious casualties to North Koreans but are eventually forced to retreat. The North Korean supply truck, driven by Chang-wu and Kap-jo and others, abruptly comes in. They cut through North Koreans and bring valuable guns to students.
The 766th’s men go into the school under the protection of tanks and take out the majority of students. Jang-Beom and Kap-Jo fight to take on the North Koreans inside the building up to the top of the building, where they have mounted machine guns. Jang-beom, Kapjo and others attempt to stop the North Koreans from reaching the roof.
As Jang-beom and Kapjo run out of ammunition, Capt. Kang as well as the South Koreans arrive. They destroy the North Korean tank and steadily defeat the North Korean infantry in the school grounds. Major Park arrives at the roof and kills Kapjo. Jang-beom is already exhausted due to his injuries and exhaustion. Park is exuberant as Jang-beom silently loads his rifle and fires at Park as Park himself. Later, Capt. Kang. Kang offers comfort to Jang-Beom while he is dying from his injuries.
The film reveals that out of the 71 students in the school, 48 were killed in defense of the school. The movie ends with a flashback, with an Army photographer taking a group picture of the student-soldiers before the regular troops leave to go to Pusan and the remaining veteran students, who are now aged, reflect on their experiences.