Taking place immediately after the events of Friday the 13th Part 3, we see Jason's body being carried off in an ambulance. At the hospital Dr. Axel places Jason's "dead" body in the freezer, then proceeds to try and get busy with a nurse. The nurse doesn't wan't any (who would with a name like Axel) and leaves him alone in the freezer room. But SURPRISE, SURPRISE, Jason isn't dead and he cuts Axel's head off with a bone saw, it just isn't Axel's night. Jason then stabs the nurse for being an ice queen to his buddy Axel. And then he's off back to Camp Crystal Lake.
And they all live long fulfilling lives.
A group of teens are heading up to Camp Crystal Lake to enjoy a night a premarital sex and various other immoral activities. They pass by a hitchhiker sitting on the side of the road. After telling them to fuck off the hitcher sits to eat a banana, which is forcibly regurgitated as Jason plunges a knife through her throat.
Tommy Jarvis plays Zaxxon on an Apple II (I think)
It turns out the group has rented a house across the street from the Jarvis residence; home of Mrs. Jarvis, Trish Jarvis, and little Tommy Jarvis (played by Corey fucking Feldman). Tommy Jarvis is your typical geek (if you're reading this you're probably just like him), and his hobby is making monster masks. Night comes and the Jarvis family goes to bed, while the teens in the other house get busy. Tommy sees two of the teens making out from his window, before his mom comes in and closes the blinds.
Morning comes, and Trish and Tommy drive down to the lake for a swim. The teens have already gotten there though, and are cheerfully skinny dipping. Tommy doesn't mind of course, but Trish drags him back to the car. But on their way home the car breaks down, this is a horror film after all, and Tommy unsuccessfully tries to fix it. Suddenly a sexy man, Rob Dyer, walks out of the forest and offers his assistance. After fixing the car, Trish offers to give Rob a ride to the lake. Turns out Rob is hunting bears and asks if there's teenagers staying near the lake.
An involuntary penis implant.
There are of course, and that night the teens get down to some real partying and SINNING, oh yeeeaahh. One girl decides to go skinny dipping in the lake, at night, alone (it's like these kids WANT to die). She swims out to a raft in the middle of lake, and while she's lying in it Jason stabs her through the abdomen. Turns out one of the guys has followed her and he swims out to the raft, sees the corpse, and high tails it back to the shore. As he clambers out of the lake Jason stuffs a spear into his crotch and lifts him into the air. Rob, camping nearby, hears the noises and runs to investigate. Too bad he left his rifle in the tent, because Jason finds it and breaks it in half.
Jimmy gets screwed.
Back at the house Jimmy (Crispin Glover), the loser of the bunch, shows his fly dance moves off to one of the girls. His mating call is successful and they retreat to the bedroom for some premarital hanky panky. One of the dudes finds an old black and white porno, so they sit around and watch that, before another couple go up to hit the showers. Jimmy comes down stairs to show brag about his achievements to his porno watching buddy, then goes to pop open a bottle of wine. Jason hands him the corkscrew, then plants a cleaver in his face. The guy watching the porno goes to make out with the screen, and Jason gives him a kiss with his knife. The couple in the shower do their business and the girl steps out for a moment. Jason steps in for her but he's a little too rough and ends up bashing the guys head apart. When the girl returns and sees her boyfriend dead, she runs for the door. Jason puts an ax through the door and the girl falls to the ground, broken hearted.
This time he's really dead. REALLY.
Rob makes it back to the Jarvis residence and warns Trish and Tommy of the danger. He decides to head over to the teens house to check things out, Trish tagging along. Inside the house they find everyone slaughtered with the electricity out, so Rob heads down to the basement to fix the fusebox. Lo and behold Jason is in the basement, and he attacks Rob with a garden claw. Trish runs back to her house and together with Tommy they barricade themselves upstairs. Jason easily breaks through the door but Trish smashes a TV onto his head. Pursued by Jason she runs through the house and manages to pick his machete up as Jason tackles her to the ground. Tommy, realizing Jason is a retard, shaves his own head to make himself resemble Jason as a child. While Tommy distracts Jason with his disguise, Trish uses the machete on him, but only manages to graze his face. Now mask less and hideous, Jason turns on Trish, but Tommy picks the machete up and slams it into the side of Jason's head. Jason falls to the ground with the machete embedded in his skull, and his face slides gruesomely down the blade.
Trish wakes up in the hospital later on, asking about Tommy. The doctors tell her that he is in shock, and send him in. Tommy hugs his sister, and glares at the camera psychotically.
Body Count: 14
Don't drop the soap.
Dr. Axel: Jason saws halfway into his neck with a bone saw, then twists his head around.
Nurse: Lifted up by her neck then stabbed in the stomach with a scalpel. Jason pulls the scalpel downward slicing through her organs.
Hitchhiker: While eating a banana Jason stabs a knife through her neck. She regurgitates the banana and pukes it out with some blood.
Samantha: Jason sticks his machete up through the raft she is lying on, getting her in the midsection.
Paul: Gets a spear-gun stuffed into his crotch, and is then lifted up by the spear.
Terri: Impaled through and through with a spear.
Mrs. Jarvis: We do not see Mrs. Jarvis die in the original release, but it is implied. In an alternate ending, seen on the Deluxe Edition, she is shown drowned in the Jarvis residence bathtub.
Jimmy: Jason sticks a corkscrew through his hand pinning it to a table, then cuts his face in half with a butcher knife.
Now THAT'S 3D.
Tina: Pulled through a window and falls onto a parked car.
Ted: Knifed in the head by Jason through the movie screen.
Doug: Jason crushes his skull against a wall with his bare hands.
Sara: While she tries to open a door, Jason, standing on the other side, sinks an ax into her chest.
Rob: Stabbed repeatedly by a garden hoe.
JASON: Tommy cuts into Jason's head with a machete. While Jason is on the ground Tommy hacks him up some more.