Brooke Storm, a little girl of about seven or eight, lives on the edge of a small town in a woodsy area, and goes to play with her dolls in an abandoned shack in the woods, on the edge of a swamp, a short distance from her house one afternoon. While she is playing, she hears an approaching motorcycle, and it stops outside. Unwilling to be discovered, she removes a loose board at the back of the shack and sneaks outside, looking in to see what, if anything, will happen. Two teenagers, intent on having sex, dismount the motorcycle and enter the shack. The girl is not quite comfortable in the shack, though, and changes her mind. Her boy-friend is predictably upset, and pulls the head off of one of Brooke's dolls in frustration. They leave, and Brooke re-enters the shack to mourn the doll. A short time later, she hears the motorcycle approach again, and, seizing the opportunity to get vengeance for her doll, gathers a bucket of mud from the swamp and steps out from behind the shack. She throws the mud in the teenage motorcyclist's face, causing him to lose control of the motorcycle and crash. Both teenagers are thrown from the motorcycle and are impaled on some long-abandoned, rusted farm implements by the roadside, where they die twitching like bugs on a pin, while little Brooke watches in horror.
Eighteen years later, Brooke is a cold, stiff, reserved high school biology teacher. She still has mental disturbances from the incident, and still lives in the same house, alone, her parents having presumably died in the interim. Her students are mostly loud, obnoxious, destructive, apathetic, and disrespectful, and she has little control over them, the stress of trying having an obvious effect on her fragile mental state. She has to pop pills to get through the day.
Meanwhile, the deaths of the teenagers many years earlier has achieved urban legend status among the current crop of teenagers, with some believing and others not, and various embellished versions of the story being passed around. They only know that two teenagers were killed there, with no details. After school one day, Coach Heaton visits Brooke in her classroom, and expresses his concern for her mental health, and asks her to come and watch the next night's football game. Brooke, however, senses that he is asking for a "pity date" and turns him down. As she leaves for the day, she meets one of the female coaches, Coach Sandy, who admits that she put Heaton up to asking her out, as she too is worried about her.
That same afternoon, one group of friends, comprised of Dickens, a troublemaker; Smiler, a fat guy; Queenie, the one girl in the group, and Jon-Jon, another troublemaker and prankster who recently quit the football team and is branded a "coward" by Coach Heaton; is trying to decide what kind of trouble to get into next while sitting in their car, and an idea comes to Dickens. He wants to prank Brooke Storm, their biology teacher. Immediately, Jon-Jon raises his objection, noting that pranking an adult, especially a teacher, was far more serious than pranking another teenager, and they would not likely get off lightly if caught. Dickens insists, though, and they drive off to reconnoiter Brooke's house, following her home.
The house is mostly two stories, but there is a section at one end that is one story. Once there, the teenagers climb onto the roof of this one-story section and look in the windows to the second story, and are treated to the sight of a naked Brooke showering. Obviously she is more comfortable at home than in the outside world. The boys enjoy the show until the phone rings, then they leave, lest they be discovered. On the phone is Coach Heaton, who tries to persuade her to come to the football game, and she changes her mind and agrees to come.
The next afternoon is the football game. We see Brooke sitting in the stands, as promised, huddled up under a scarf and sunglasses, obviously ill-at-ease. The football team is overmatched and outclassed, making many poor plays and falling behind 20-0. Our four miscreants are out in the parking lot, kicking around ideas for the prank on Brooke, when they decide to prank the football players. While the game is in progress, they drive out of the parking lot and onto the football field, where Jon-Jon, who recently quit the team, stands up in the passenger seat and "intercepts" the quarterback's pass. They drive doughnuts around the field, with Jon-Jon standing up triumphantly holding the football, before driving away, football and all. They have made a mockery of the game, but the crowd in the stands found it far more entertaining than watching the home team lose. Even the opposing football players think it's hilarious. In the evening, Coach walks Brooke to her door, hoping to be invited inside, but she does not do so. Coach walks away, muttering to himself that if he had been able to win the game, he might have gotten laid.
The four miscreants have a plan for their prank. They drive to the swamp, where the motorcycling teenagers died 18 years before, to gather mud, where Queenie reveals that even though Dickens is the leader of their group, she is more interested in Jon-Jon romantically. With several bags of mud, they drive to Brooke's house, where she is grading papers, mostly F's. They don masks, lest they be recognized, and climb onto the roof again. When they are all in position, they begin stamping on the roof and throwing mud on the windows below. The noise, and especially the mud, brings back Brooke's unpleasant memories immediately, and she is immediately frightened. She opens the door to investigate, and is splattered with mud herself. Then she freaks out completely and retreats back inside. Dickens is emboldened to escalate the prank, and breaks the windows on Brooke's door, but an approaching car frightens all four teenagers away, back to their own parked car. The visitor is Coach Sandy, checking on Brooke. She discovers the mud, the broken glass, and a freaked-out Brooke, but can't do anything for her except clean her up in the bath and give her a Quaalude to settle her frazzled nerves.
After Sandy leaves, Dickens, who never went all the way back to the car, returns to the house and enters through the broken door, while his friends wonder where he went. Dickens goes to Brooke's bedroom, where she is laying semiconscious from the Quaalude, and begins fondling her, apparently thinking about raping her. Eventually, the friends in the car lose patience, and Queenie goes to look for Dickens, and finds him inside, and is immediately disgusted by what she sees. Nevertheless, she pushes Dickens away and begins fondling Brooke herself. Perhaps she bats for both teams.
Jon-Jon and Smiley enter a minute later, looking for Dickens and Queenie, and they too are repulsed by what they find. They realize that the prank has already gotten far out of hand, and there is noticeable friction especially between Jon-Jon and Dickens. While they are all arguing amongst themselves, Brooke comes slightly out of her drug-induced haze, sees the chaos around her, and escapes by jumping through her second-story window onto the ground below. The lingering effects of the Quaalude and the shock of the fall knock her out again, and the dismayed teenagers think she is dead. Jon-Jon and Dickens get into a fistfight.
The teenagers start to drive back towards town, but they know they are in for a lengthy jail sentence if they are caught, so they start scheming to divert the blame for the incident elsewhere. They decide to frame the football team's quarterback, not known to be very bright, for the break-in and vandalism. Knowing that he, with the rest of the team, will be at the diner following the game, they send Jon-Jon in the car back into town to steal something of the quarterback's to plant at Brooke's house, and return a short distance to the house themselves on foot, to wait.
While they wait, there is much argument over how far overboard the prank has gone, especially between Dickens and Queenie. Smiley belatedly notices that their fingerprints are probably all over the house, and panicking, tries to wipe down anything he thinks they might have touched. Queenie leaves the house to find her own way back to town. Around this time, Brooke has woken up on the front lawn, and starts talking softly to Queenie. Queenie is overjoyed that Brooke is alive, knowing that they won't be blamed for killing her, but as soon as she turns her back, Brooke knocks her down with a large rock, and then uses the rock to repeatedly smash Queenie's face and skull, until Queenie's head is a barely recognizeable mess.
Meanwhile, Jon-Jon arrives at the diner's parking lot, and finds the quarterback's car. Mindful of being seen, he keeps low to the ground and sneaks over to the car, and reaches in and removes the quarterback's jersey, then flattens one of the tires on the car. He returns to his own car, but his exit is deliberately noisy, and the football players in the diner notice him and recognize his car. Thinking he is up to something, they go outside to look and notice the flat tire. The quarterback and one of the other players pursue Jon-Jon on the second player's motorcycle. In order to frame the quarterback, Jon-Jon had to remove the quarterback's alibi by enticing him to leave the diner, but now he has to find some way of shaking them off so that they cannot follow him back to Brooke's house and discover what is going on. After a lengthy drive, Jon-Jon makes an abrupt U-turn and drives back toward the pursuing motorcycle, forcing it off the road, where it crashes into a parked car, causing an explosion. The quarterback and his friend were able to ditch before the crash, so they survive with only bruises, but are miles from town without transportation. Jon-Jon, free from his pursuers, can now return to Brooke's house.
At Brooke's house, Dickens and Smiley are getting more and more antsy, thinking that Jon-Jon should have returned a long time ago. Smiley thinks that something happened to Jon-Jon and he wasn't able to complete the plan, and they had better start thinking of a new plan, as time was slipping away. They don't notice when, some time later, Jon-Jon arrives back at the house, and they don't notice it when he hears Brooke's voice outside as Queenie did, and goes off to investigate rather than going inside right away. Brooke ambushes him, and hits him with the rock, and he goes tumbling down the hill behind the house. Brooke returns to the house unnoticed, entering through the back, and takes a knife from the kitchen drawer and goes off to make her next move.
Smiley thought he heard noises outside, and goes out to check. He sees the car, but no sign of Jon-Jon. He goes back inside to tell Dickens what he saw. Dickens becomes even more flustered, realizing that nothing he is trying to do is going even remotely according to plan, but Smiley feels sick and goes upstairs to find a bathroom. Brooke is there, and buries the knife in Smiley's head. He falls back down the stairs at Dickens' feet. Brooke then charges Dickens with another knife. Dickens tries to escape but he is pinned to the wall with the knife. Brooke ties him to the wall by his arms.
Outside, Jon-Jon gets up from the forest floor. He was hit only once and knocked out, but now he is awake again, and returns to the house. There he finds Brooke reading from a biology textbook with a scalpel in hand, apparently intending to dissect Dickens like a laboratory experiment, while Dickens is begging to be released. Jon-Jon enters the room, pushes Brooke away and releases Dickens. Jon-Jon wants to leave at once, but Dickens picks up the knife, intending to kill Brooke with it. Brooke picks up a long poker and holds it out just as Dickens jumps at her, and Dickens impales himself on the poker. However, as he does so, he is able to sink the knife into Brooke's throat. Both are dead.
Jon-Jon, the sole survivor, returns to the car, gets the stolen jersey, and plants it in the room, hoping that this part of the plan at least, would work. He returns home, but the stress has clearly taken its toll on him. He watches static on TV all night, unable to think of anything.
The next day is another school day, and Brooke doesn't show up for work, for obvious reasons. There is a substitute teacher in biology, who has a vaguely similar appearance to Brooke, and while being somewhat firmer, is still unable to command the respect of the students. Jon-Jon, still appearing shell-shocked, is unable to concentrate. As he looks out the window, a police car arrives, and two policemen get out and enter the school. A short time later, they enter the biology classroom, and immediately arrest the quarterback, taking him away without even reading him his rights. Jon-Jon is amazed that something finally went right, and the frame-up worked, at least so far. Still, he cannot concentrate, continuing to look out the window even after the policemen have driven away, unable to think of anything except what happened the previous night. When the substitute teacher confronts him, he looks at her, and she reminds him so much of Brooke that his mind finally snaps, he begins having flashbacks and screams loudly enough to be heard throughout and outside the school building.