IF YOU WANT to see a film that will truly scare you, forget "The Texas Chainsaw Massacre" or movies of that ilk. "Zero Day," clearly inspired by such events as the Columbine High School shooting rampage, will chill you to your core.

Written by Ben Coccio and Chris Coccio and directed by Ben, "Zero Day" plays out as a series of video diary clips taped by high school students Andre and Cal.

As you learn immediately, Andre (Andre Keuck) and Cal (Calvin Robertson) are planning to carry out an attack on their school. Calling themselves "the Army of Two," they're making these video diaries as a record for when they've completed their "mission."

The beauty of the movie is in how despite their efforts to be profound, menacing and, the holy grail for teenage boys, cool, their inherent youthfulness always creeps in. When, for example, they're acting out "today's episode of 'Home Gun Review' " and demonstrating how to make a gun easy to conceal by shortening its stock, the family cat wanders into the scene. As it ends you hear Andre say to the cat, "Don't tell Dad, okay?"

Similar moments -- such as when Cal, observing the camo-wearing Andre blending into the bushes, exclaims "Dude! Camouflage really works!" -- underscore their youthful humanity and also inject a bit of humor into an increasingly tense march toward their goal.

The cast of nonprofessional actors brings an unnerving authenticity to the film. Keuck (who's an undergraduate at George Washington University) and Robertson have a naturalness that makes you say, "Oh yeah, I knew a kid like that in high school." Their parents make lame jokes and give them occasionally awkward but clearly loving support. They detest the captain of the wrestling team, Brad Huff (and his Range Rover), because as Andre puts it, "He's everything we hate in one handy little form." They kid each other about prom dates or the lack thereof. And it's clear that like almost every teenage male throughout time, they have a longing, unspoken but lurking just under the surface, for some semblance of control over their lives.

Watching this well-crafted gem of a film, you realize that these two would-be mass murderers aren't abnormal. They're quintessentially normal, like thousands of other kids, and that's what makes "Zero Day" the scariest movie of all.

ZERO DAY (Unrated, 92 minutes) -- Contains obscene language and violence. At Visions Bar Noir.

Andre Keuck as a teenager who plots a school massacre in "Zero Day."