Day Zero

The film, told almost exclusively through Andre's video camera, begins with the introduction of Andre Kriegman and Calvin Gabriel announcing their intention to assault their high school, calling their plan "Zero Day". They keep a video diary on the camera, carefully hiding this from their friends and families. The majority of the film depicts the boys planning, preparing, and explaining some of their motives. There are also unrelated scenes such as the boys at a party, egging the house of someone they dislike, and Cal going to the prom while Andre works at a pizza place.

The final scenes of the movie show the boys arriving at school on May 1 and preparing their weapons in the car. They then run into the school, armed with three pistols (a Ruger GP-100 .357, a Glock 17, a Revolver), an M1 Carbine, a 12-gauge pump action shotgun, and at least twenty pipe bombs. The entire shooting is shown through the eyes of security cameras. Making their way through the school, Andre and Cal eventually watch law enforcement arriving in large numbers outside. After arguing over whether or not to shoot at the police, Andre and Cal decide to count to three, then shoot themselves.

The next scene is set on May 10, nine days after the shooting. A group of youths film themselves going to a park where memorial crosses have been set up. The youths reveal that Andre and Cal killed 12 students and themselves. They find Andre and Cal's crosses and set them on fire before running back to the car. The last scene shows the two crosses on fire before cutting to the credits