In the opening black and white sequence, a teenage girl with a hood on walks into a burger joint, she orders and the cashier has a startled look when she sees her. When the girl walks into the restaurant everybody in the room is looking at her. A boy in the room asks his mom "Why does the lady look like that?" The boy's mother tells him to stop for everybody now is staring at her. It is revealed that the girl has a distinctive burn on one half of her face. Suddenly, she yells at them to stop staring and says she did not choose to look that way. Sometime earlier...
a South Asian boy, named Ravi, is constantly being bullied by a much larger tormentor in class. Another scene shows a nerd Goth girl named Emily, who is by her locker, is approached by three girls, named Kelly, Bridget, and Heather, who emotionally attack her and taunt her for crying. A little later, two teen nerd boys, Jack and Dane, are in a field setting up bear traps. At lunch, the outcast students are all sitting quietly at a lunch table until one of the bullies throws his milk box on one of the bullied kids books. He approaches him, giving back his milk box. Another kid named Kurtis, who is friends with both the outcasts and the popular group, approaches the group of people and invites them to one of his video shoots on Friday.
The outcasts talk among themselves and say they like him and they tell each other to make sure Kurtis does not end up being at the party. The next scene shows their home life. Dane talks to himself and points a gun at his own head while in his bedroom, while his uneducated and negletful parents fight downstairs. Another scene shows Ravi at home with his suttle and emtionally barren Indian family; a depressing quiet life where nobody talks or even looks at each other except for the house maid. Emily's mother is a shrewed and divorced woman who pays little attention to her.
Jack, whom is a talented banjo player, has a divorced mechanic father who ignors him all the time. At the video shoot, Bradley and Tommy both confront Ravi and Dane in the boys room, and break Ravi camera for no reason. Bradley tells Dane that he bullies him because he will not do anything about it. Afterwords, Ravi tells Kurtis about what happened and Kurtis warns Bradley to leave Parker. The beligerent Bradley refuses and starts a fight wtih Kurtis, fed up with the egotistic boy's attitude. Jack, leaving his home, is talking to his father who is a mechanic working on his car, about what he is going to do. He tells him that he has a letter about it and that he'll probably be angry. The father, obviously ignoring him, continues on working as Jack leaves.
At night, Bradley and two others are pulled over by the cops on their way to a party, and are caught smoking marijuana. They are let go after getting almost all their weed confiscated. Meanwhile, the group of outcasts are around a fire talking about hell and doing God's work in tormenting their tormentors. They put on costumes and blend in with a costume filled house with a hidden camera. They then lace a punch bowl with chloroform causing everyone to pass out. Sometime later, the people in the party awaken to a loud noise from a boom box. They find themselves chained together, with the five outcasts all masked and wearing costumes inspired by horror movies (Killer Klowns from Outer Space, The Strangers, My Bloody Valentine, The Mummy, etc). They want revenge for the years of torment and want to torture their worst enemies.
A vulgar teenager, named Miles, decides that the entire thing is a stupid Halloween joke and starts to mouth off. As a result, Jack applies a cattle gun to his face and knee, severly wounding him and disfiguring his face and knee. One boy, Tommy, is allowed to go and get help, but his escape is cut short when he steps into a bear trap in the woods and is caught by a group of three boys riding on dirt bikes nicknamed "The Triplets", who help the outcasts. Tommy is brought back to the house and thrown into a room with the wounded Miles. Another tormenter, a popular jock named Bernard, is next as he defiantly mouths off to the group (clearly a defiant sociopath, daring them to kill him). Bernard is tortured first by Ravi who stabs him in his shoulder with a knife, and pours a liquid drug down his throat that attacks his muscular system, keeping him from moving or speaking.
Emily then tourturs him by stabing him in his face and neck with hot-tipped needles. Kurtis, who attended the party after all, is secretly given a key by Ravi and luckily escapes. Ravi is then stabbed by Dane and killed almost instantly, for betraying the group. Heather is the next victim as she is tied to a chair and Emily smears a paste on Heather's face that is made to slowly start disintegrating the skin it touches, leaving Heather horribly scarred. It is here that Bridget realizes that it is Emily and apologizes.
Emily offers Bridget the chance to be spared by cutting off Bradley's fingers, but she refuses. Emily then offers Bradley safety if he agrees to cut off Bridget's fingers. Bradley cuts off two fingers on Bridget's right hand before Emily offers the deal to Bridget again. Bridget reluctantly agrees to cut off Bradley's fingers. Ultimately, she decides she cannot harm her friend and is punished by Emily, who smears the previously-used acidic compound on her face. Meanwhile, Kurtis makes it to a neighbor's house, an elderly ex-soldier named Parker.
He is suspicious of the fact that Kurtis showed up with a gun. On top of all that, Parker is a racist and seeing a black teenager on his property makes him tie up Kurtis for a long period before Kurtis finally convinces him that there really is trouble at the old house in the woods. Remembering meeting two of the kids earlier the previous day and seeing them set up bear traps in the grass, decides to investigate, leaving the tied up Kurtis behind. Parker goes to investigate, but is caught in a trap, severely injuring his legs.
Despite the injuries, he manages to get himself free and kills two of the triplets as they are riding around him on their ATV's. Back at the house, Bradley (still tied up in the chair) is taunted by a now very insane Dane whom by this time has revealed his face to his captives. Bradley, now breaking down into a sobbering coward, attempts to apologize, though this bears no fruit. Dane then uses his switchblade to sever Bradley's spinal cord, instantly paralyzing him from the neck down. Back at Parker's house, Kurtis manages to untie himself and calls the police from Parker's house phone to report what is going on.
Kurtis then returns to Dane's house, where he saves a boy, named Riggs, from getting his tongue cut off. However, Kurtis is shot in the arm by Dane after he manages to kill Andy, one of the other outcasts. Dane is about to finish the job, but he is shot and killed by Emily, who has had enough. After one last hug, and Emily speaking her final words to Kelly. Jack then shoots and kills Emily, just as the police arrive. The police burst through, demanding that Jack drop the gun, but he only points it to his own head, declaring that they are "too late" and that "there are more of us out there" before pulling the trigger, killing himself.
A news report recounts how the popular kids were abducted and tortured "without reason". Kelly, who remained unharmed, swallows a large amount of pills in the school's restroom. At school, Kurtis exchanges looks with the remaining triplet. The final scene reveals that Bridget is the disfigured girl from the beginning of the movie..