On April 20, 1999, two Columbine High School seniors walked into their own school with guns and homemade bombs and killed twelve students and a teacher before turning their weapons on themselves. This film reconstructs the massacre and the year of planning behind it, drawing on journals, home videos, police records, and interviews to trace how Eric Harris and Dylan Klebold moved from ordinary teenage frustration to a meticulously rehearsed attack. It looks past the initial "bullied outcasts" narrative that dominated early coverage, weighing psychological assessments that describe Harris as showing signs of psychopathy and Klebold as depressive and suicidal. Investigators and behavioral experts walk through the warning signs missed by parents, teachers, and police in the months before the shooting, including a sheriff's file opened on Harris a year earlier. The film treats Columbine as the template later shooters studied, asking what made these two specific teenagers act rather than simply cataloguing the horror of the day itself.