The film looks into the nature of violence in the United States, and explores what Moore suggests are the causes for the Columbine High School massacre and other acts of violence with guns. Moore focuses on the background and environment in which the massacre took place and some common public opinions and assumptions about related issues.
Moore attempts to contrast this with the attitude prevailing in Canada, where (he states) gun ownership is at similar levels to the U.S. He illustrates his thesis by visiting neighborhoods in Canada near the Canada-U.S. border, where he finds front doors unlocked and much less concern over crime and security.
Moore also takes two Columbine victims (Mark Taylor and Richard Castaldo) to the American superstore K-Mart headquarters in Troy, Michigan, ostensibly to claim a refund on the bullets still lodged in their bodies.