At Camp Manabe, a New York state summer camp, shy overweight camper Alan (Michael Gibney), who gets the smallest fart lighting, threatens Eddie (Miles Thompson), Mark (Tommy John Riccardo), Billy (Dino Roscigno) and Pee Pee (Paul Iacono) after embarrassing himself, who was soon stopped by camp counselor Randy (Brye Cooper).
The next day, Alan later confronts Randy for some ice cream, who is then allowed to go the kitchen by Ronnie (Paul DeAngelo) so as not to exaggerate the fight, in which later on Alan is beaten up by the assistant cook Mickey (Lenny Venito) by throwing eggs at him. Alan then throws a butcher knife at Mickey and the camp owner, Frank (Vincent Pastore), as well as the head cook Charlie (Isaac Hayes) seeing what he did, argues with Alan because he was already irritated by his misbehavior. Alan, suffering from rheumatic fever, runs away feeling rejected, with his stepbrother Michael (Michael Werner) chasing after him. After being threatened, Michael goes back to the camp, telling Alan that he does not care what he does any more. In the kitchen, Mickey is then killed when he is dumped into the deep fryer by an unseen person while cooking fries for dinner and later his body is dumped in the trash compactor.
During the social, Alan is fooled by fellow stoners Weed (Adam Wylie) and Stan (Chaz Brewer) into smoking dried cow manure, mistaking it for marijuana which makes him cough and falls on Stan's crotch, earning him the nickname 'blowjob'. After the social, Weed is tied to a chair by the unseen killer and gas is squirted down his throat. The killer then sticks a lit up cigarette in his mouth and his insides explode.
Ronnie starts to suspect that the murders that happened 20 years ago are happening again. Frank, in an attempt to ignore bad publicity, states that the murders were accidental and the camp continues to go on with its normal activities.
Meanwhile, the local sheriff, Jerry, meets with a certain Ricky Thomas (Jonathan Tiersten), the stepbrother of the killer Angela from the first 'Sleepaway Camp' movie to question him about Angela who may be behind the recent deaths at the local camp. Ricky claims that Angela has been locked up in the local lunatic asylum for the past 20 years and that the last time he visited her was three weeks ago. Sheriff Jerry (who speaks through a voice-box because of having throat cancer) tells Ricky that he will keep in touch.
One week later, Alan is further bullied by being shot during a paintball game by all the players. In order to steal Karen (Erin Broderick) away from Alan, Michael makes Alan look like a psychopath. He is again bulled by campers T.C. (Christopher Shand) and Chooch (Lucas Blondhelm) by giving him a wedgie in front of everyone at the waterfront. That night, Michael, T.C. and Marie (Samantha Hahn) force Karen to lure Alan to the back of the stage, where they take his clothes off, tie him up, blindfold him and embarrass him in front of everyone at the social.
Ronnie suspects that counselor Peter (Kate Simses) is the killer for appearing everywhere when Alan is in trouble. Suddenly, T.C. and nine others start calling Alan "Blowjob", which causes him to be in his rheumatic state and runs off into the night. After returning to his cabin, Frank is knocked unconscious with a hammer and wakes up with his head inserted in a birdcage. The unseen killer opens up the birdcage, places two rats inside and locks it. The rats eat through his head and exit via his intestines.
Meanwhile, Randy and Linda (Jackie Tohn) go to the pump house to have sex. While Randy is urinating, the killer ties him to a tree, using fishing line as a noose to wrap around his penis. Suddenly, Linda sees the killer and drives off in the jeep, where the fishing line is tied to the jeep and, while driving at 85 mph, pulls Randy's penis off. Linda continues to drive, before crashing at a wrapped barbed wire that is caught on her face.
In the camp, T.C. has been grounded for the rest of the summer for bullying Alan. Suddenly, a wooden spear comes through the floor and impales T.C. in the eye, with Spaz (Jake O'Conner) as a witness.
Meanwhile, Ronnie and Jenny (Jaime Radow) find Frank dead in his office. Ronnie and Jenny begin rounding up everyone left in the camp, thinking that the mysterious Angela has return and is the one responsible for all the murders. Bella (Shahida McIntash) goes back to her cabin where she finds that the bunk above her has been replaced with spikes. The killer, who is also in the cabin, jumps down from the rafters and lands on top of the top bunk, causing it to fall on Bella, piercing her with the spikes. Soon, T.C. and Bella are found dead and after the counselors leave, Ricky Thomas arrives at the camp having been called by Sheriff Jerry, while Karen, who is wandering around feeling bad about Alan, bumps into the killer and faints.
Karen wakes up at the Rec Hall with a rope hanging from a basketball hoop tied around her neck. The killer flips a switch to raise the net, causing Karen to be lifted off the ground. Michael comes in before Karen is killed and lowers the net while Sheriff Jerry also arrives to help Karen down. After Karen tells him that she thinks Alan is the killer, Michael grabs a mallet and goes after Alan, which he beats him with the mallet. Suddenly, the real killer appears behind Michael as the screen fades to black.
Ronnie, Ricky and Jenny find a fatally wounded but still alive Alan on the ground. As Ronnie tries to get information out of Alan, Sheriff Jerry comes up behind Ronnie and Ricky, explaining that he's been waiting a long time for this, and then, the sheriff pulls off his hat, and a false prostectic face, nose, sunglasses, fake beard and it's revealed that Sherriff Jerry is Angela Baker (Felissa Rose), the serial killer from the very first 'Sleepaway Camp' movie. Soon, Ricky, Jenny and Ronnie find a nearly-dead Michael skinned alive on the ground as Angela laughs maniacally at them. She then looks at the camera with a vicious expression on her face, breaking the fourth wall.
After the ending credits are over, a clip is shown three weeks prior to the events at the of the film. It shows that Angela had escaped from the psychiatric clinic that she'd been locked up in for the past 20 years. When her stolen car broke down form a gas leak, she pulled over and flagged down Sheriff Pete (Carlo Vogel), the real sheriff, while dropping the car on his head, stealing his clothes and becoming the new sheriff.