Alan (Michael Gibney) is a boy who is at a summer camp. The movie shows that Alan is a bully, who in turn is bullied by other kids. Among his abusers are his stepbrother Michael (Michael Werner) and his friends Vinny (Christian Hess) and T.C. (Christopher Shand), and the girls at the camp, mainly a girl named Bella (Shahidah McIntosh). Several boys are lighting farts one night. Alan tries, and after failing, he threatens the other boys, but is soon stopped by camp counselor, Randy (Brye Cooper). In the dining hall, Alan gets into a violent confrontation with Randy after he complains about the food. Ronnie allows Alan to get something else to eat, but Alan gets in trouble with cook Mickey (Lenny Venito). Alan throws a butcher knife at Mickey and the camp owner, Frank (Vincent Pastore), argues with Alan. Alan runs away, with Michael chasing him. In the kitchen, Mickey is killed after being held above and dumped into the deep fryer. His body is dumped in the trash compactor.
During the social, Alan is fooled by campers Terry (Adam Wylie), nicknamed "Weed", and Stan (Chas Brewer) into smoking dried cow manure, which makes him cough and falls on Stan's crotch, earning him the nickname "Blowjob." After the social, Weed is tied to a chair and gasoline is squirted down his throat. The killer sticks a lit cigarette in his mouth and his insides explode. Ronnie suspects the murders that happened twenty years ago are happening again, but Frank states the murders were accidental. A week later, Alan manages to convince two girls, Karen (Erin Broderick) and Marie (Samantha Hahn), to go to his "secret hideout". Michael makes Alan look like he skinned frogs, and Karen and Marie run away. Michael, T.C. and Marie 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 at the social.
Ronnie suspects that counselor Petey (Kate Simses) is the killer for always being nearby when Alan is in trouble. After returning to his cabin, Frank is knocked unconscious with a hammer and wakes up with his head inserted in a birdcage. The killer opens the birdcage and places two rats inside the cage. The rats eat through his head and down into his intestines. Randy and his girlfriend Linda (Jackie Tohn) go to the pump house to have sex. Whilst Randy urinates, the killer ties him to a tree, using fishing line to wrap around his penis. Upon returning, Linda panics after hearing Randy placate the killer and drives off in the jeep, but the fishing line is tied to the jeep and tears off Randy's penis. Linda crashes after driving through a wrapped barbed wire line, which wraps around her face.
After Vinny visits T.C., a wooden spear comes through a hole in the floor while T.C. is looking into it and impales him through the eye. Ronnie and another camper, Jenny (Jaime Radow), find Frank dead and begin rounding up everyone. Bella goes to her cabin, where she finds that the bunk above her has been replaced with a board with spikes. The killer jumps down from the rafters and lands on the top bunk, causing the spikes to impale and kill Bella. T.C. and Bella are found dead and Ricky Thomas (Jonathan Tiersten), Angela's cousin, is called by Sheriff Jerry. Karen runs through the camp. She finds Randy and Linda dying before bumping into the killer and fainting.
Karen wakes up 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 arrives, causing the killer to run off, and lowers the net. After Karen tells him she thinks Alan is the killer, Michael grabs a croquet mallet and runs to Alan's secret hideout, where he finds Alan, and starts beating Alan with the mallet. However, the real killer appears behind Michael as the screen fades to black.
Ronnie, Ricky and Jenny find a badly wounded Alan. Sheriff Jerry walks up, explaining through his mechanical voice box that the victims never learned, were always so mean all the time, could do whatever they want and get away with it, and they got what they deserved. Sheriff Jerry reveals himself to be Angela Baker, the killer, which causes Ronnie to say "I knew it was you". Jenny finds something on the ground and runs away screaming. Ronnie and Ricky investigate and find Michael skinned alive on the ground. The film ends with Angela laughing maniacally before suddenly stopping and staring evilly into the camera.
Following the credits, three weeks prior to film, Angela escaped from the psychiatric clinic. She causes a brake fluid leak in a car and flags down Sheriff Pete (Carlo Vogel), the real sheriff. She murders him by dropping the car on his head and steals his clothes to become the new sheriff.
Return to Sleepaway Camp wrapped filming in 2003 and was scheduled to be released theatrically between 2004 and 2006, but due to unsatisfactory CGI effects and a lack of distribution deals, it did not see release until November 2008. An executive producer of the film, Thomas E. van Dell, claimed that most of the corrected CGI had been completed by December 2006, but the director, Robert Hiltzik, felt that it needed more work to meet his expectations. By 2007, compositors and CGI personnel had been hired by van Dell to correct the effects. Additionally, a small special F/X group was hired to reshoot work unapproved by Hiltzik; such included the skinned body of the character Michael, additions to the death of camper T.C., and unfinished/pick-up shots. All work was finished by 2008, and the producers secured distribution through Magnolia Pictures. The film was released direct-to-video in the United States in November 2008, and was released internationally in 2009.
A 2/5 was bestowed by David Harley of Bloody Disgusting, who regarded Return to Sleepaway Camp as a draggy, unimaginative, and unfunny film with an ending "that manages to disappoint with its banality". Dread Central's Brad Miska gave Return to Sleepaway Camp a 1½ out 5, and summarized his review with, "Gone is the really black humor of the first film. Gone is the insane twist. Gone are the inventive kills. And gone is nearly all of the charm that has kept this franchise alive. I would have rated this even lower if not for the nostalgia factor. Man, what a letdown". In his review for DVD Verdict, Gordon Sullivan stated, "Return to Sleepaway Camp makes Sleepaway Camp III: Teenage Wasteland look like Shakespeare. A poor script, a total lack of compelling campers, and a too-brief glimpse of Angela all spell trouble for this nostalgic trip back to camp-land. I know that diehard fans of the original film will likely get suckered into watching this, but everyone else should stay far, far away". A 1/4 was awarded by Arrow in the Head's Pat Torfe, who concluded, "A 'return' this is not. Hiltzik should've taken Sleepaway Camp IV's demise as a warning and let this series go quietly. Return is nothing what the original trilogy was in terms of kills or fun. It limps by on sloppy editing, unlikeable characters, unsatisfying kills and hopes that people get pulled in by the return of past characters".