At first blush, "Mean Creek," by first-time writer-director Jacob Estes, is a film in the tradition of "River's Edge" and "Stand by Me." And on its surface, this engrossing exploration of friendship, loyalty and personal ethics has much in common with those beloved coming-of-age dramas. But in its seriousness and willingness to take on questions of daunting moral heft, it joins such classics as "Heart of Darkness" and "Lord of the Flies." As such, "Mean Creek" is that rare movie that manages to be not only an adroit, carefully observed study in character and suspense, but important.

Rory Culkin (seen in the wonderful "You Can Count on Me") plays Sam, a mild-mannered middle schooler whom we meet in the midst of one of his routine beatings by the playground bully, George (Joshua Peck). Once Sam's older brother Rocky (Trevor Morgan) learns of the daily humiliations, he takes a protective interest; later, Rocky hatches an idea with his pals to help Sam get revenge on the universally despised George.

But that plan must meet Sam's own discerning ethical standards; as Rocky's friend Marty (Scott Mechlowicz) says, "Sam's a regular little Gandhi." "Yeah," Rocky responds, "he's a little white Martin Luther King." Even at 13, Sam is wise enough to know that the best revenge is that which doesn't plunge you into the same spiritual muck as your oppressor. So the boys hit on the karmically perfect scheme, one that serves as mortifying comeuppance for George even while qualifying as a relatively harmless prank. The guys set off -- with friend Clyde (Ryan Kelley) and Sam's new girlfriend Millie (Carly Schroeder) -- on an adventure that is equal parts wicked and innocent and that, inevitably, turns out quite differently than planned.

Estes ratchets up the tension and dread to a masterful degree in "Mean Creek," much of which transpires on videotape, giving the story an intimate sense of urgency. As he follows the kids into what starts out as a carefree, if mischievous, Saturday, the gloom gathers and grows as each character's motivations subtly shift. (The movie's mood of anxious rootlessness is amplified by the largely parent-free universe these young people seem to inhabit.)

George, an admittedly unattractive and off-putting creature, may be a dangerously aggressive jerk or a pathetically harmless putz; likewise the volatile Marty, under whose charismatic leadership the group naturally falls, may be a loose cannon or a victim suffering from his own psychic wounds. Throughout "Mean Creek," the emotional fallout of their actions plays eloquently across the faces of the youngsters -- especially Sam and Millie, who serve as their elders' comic foils as well as their collective superego. The fact that so much of what they're doing is interior would give veterans twice their age pause; these gifted young actors do an admirable job of embodying characters who are visibly and painfully wrestling with every choice they make.

Those choices are eventually put to the supreme test, and even though that pivotal event is a bit contrived, its aftermath is so brilliantly conceived and staged that Estes can be forgiven for reaching just a bit. As incisively as he evokes the tribal rituals of aggression, posturing and competition of a boy's life, the filmmaker takes just as much care in reflecting their psychic toll. Observing Sam and Rocky as they try to be men of action -- while their thoughts keep getting in the way -- is akin to watching time-lapse film of a plant growing and stretching into the sun.

The film's most memorable scene, when the characters scatter -- individually retreating into agonizing confrontations with their own consciences -- is made all the more extraordinary by Estes's willingness to let it play out at length, entirely in silence. Like Gus Van Sant's "Elephant" last year, "Mean Creek" subverts the expected tropes of cautionary tales about youthful misbehavior. Instead Estes has created an altogether original, and deeply troubling, portrait of moral evolution. It's a measure of this promising filmmaker's humanism that, for each of those characters, compassion comes more naturally than cruelty. It's a measure of his intellectual and artistic honesty that even their best impulses are occasionally swamped by the darker forces of their own natures. Rather than offer warming fictions about redemption and rough justice, "Mean Creek" leaves viewers chilled to the bone, as it should. It doesn't end happily, but it ends well.

Mean Creek (87 minutes, at Cineplex Odeon Dupont Circle and Landmark Bethesda Row Cinema) is rated R for profanity, sexual references, and teen drug and alcohol use.

Joshua Peck, left, is a playground bully who becomes a victim in Jacob Estes's "Mean Creek."