May 1980, in the Songam-dong area of Gwangju, the sound of gunfire rings out, bang, bang, bang...! A mistaken engagement occurs between the 11th Airborne Brigade and the Army Training Center's instructor troops. After 9 soldiers are killed, their guns are turned towards innocent citizens. May 2023, the sounds of that day, boom, boom, boom... are revived on screen! The camera meticulously records and traces the timeline of that day. And one question: Why did they pull the trigger?