- "They were warned... They are doomed... And on Friday the 13th, nothing will save them."
In a brief prologue set in 1958, two summer camp counselors at Camp Crystal Lake, named Barry (Willie Adams) and Claudette (Debra S. Hayes), sneak away from a campfire sing-along to have sex. Before they completely undress, an unseen assailant sneaks into the room and murders them.
The film moves forward to the present: Friday, June 13th. A young woman named Annie (Robbi Morgan) enters a small diner and asks for directions to Camp Crystal Lake, much to the shock of the patrons and staff. A strange man, Ralph (Walt Gorney) reacts to the news of the camp's reopening by warning Annie that they are "all doomed". Enos (Rex Everhart), a friendly truck driver from the diner, agrees to give Annie a lift to the crossroads cemetery, which is halfway to the camp. During the drive, he warns her about the dark, bloody history of the "Camp Blood" and insists she quit immediately. Informing her of a boy drowning in 1957, the two murders and serial arson as reasons why the camp is considered cursed. Annie ignores the superstition and continues her hike to the camp when dropped off at the cemetery. Annie hitches another ride further down the road with an unseen driver. She starts to panic when the driver speeds past the entrance to the camp and jumps out. The driver chases the injured girl into the woods, catching her and slitting her throat. At Camp Crystal Lake itself, Alice (Adrienne King); Bill (Harry Crosby) and Brenda (Laurie Bartram) are busy refurbishing the cabins and facilities with Steve Christy (Peter Brouwer), their demanding owner. They are joined by the new arrivals, Ned (Mark Nelson); Jack (Kevin Bacon) and Marcie (Jeannine Taylor). With only two weeks left until the camp opens and much work to be done, Steve pushes his new counselors to work fast. As the day goes by and Steve leaves for town to stock up on supplies, the counselors play as various odd things happen. Ned skips out on his jobs to play archery, almost hitting Brenda. Alice finds a snake in her cabin, which is killed with a machete. All the counselors go swimming in the lake for some relaxation and Ned ruins it by pretending to drown. They get a visit from an arrogant Officer Dorf, who arrives to search for Ralph, hassles the counselors and warns the group to stay out of trouble. Ralph, who was hiding in the kitchen pantry, again tries to warn them of their impending fate. All this happens as the killer watches from afar, only identified by a pair of black slacks; brown plaid shirt and a class ring. As a storm starts heading towards the lake, the killer heads into one of the cabins to hide, wearing a black rainslicker. Ned spots the killer, and follows him into the cabin to investigate.
Later that evening as the storm hits, Jack and Marcie go into the cabin to have sex, unaware that Ned's body is in the bunk above them, his throat slit. Marcie leaves Jack to use the restroom, leaving him alone with the killer, who has been under the bed the entire time. The killer grabs his head and forces him down while ramming an arrow through the bed, piercing his throat. The killer heads to the bathrooms and draws Marcie out of the shower, slamming an axe into her forehead.
In Alice's cabin, Brenda becomes bored with nothing to do and, with the help of weed and beer, decides Bill and Alice should play "Strip Monopoly" with her to pass the time. When the savage storm blows the door open halfway through the game, Brenda realizes her cabin windows are open and heads out to shut it, calling it a night. As Brenda gets ready for bed and curls up with a book, a child-like voice calls out to her from the storm. Unsure if it is another person or a serious call for help, Brenda gives in and heads outside into the rain. The outdoor lights come up, revealing she has walked into the archery range. Blinded by the light, she is trapped by the killer and dies offscreen.
When Bill returns to Alice's cabin after a quick venture outside, Alice tells him she heard a scream, certain it was Brenda's. The two of them head out to Brenda's cabin, where they find a bloody axe (the same one used to kill Marcie) tucked away in Brenda's bed. Searching Jack and Marcie's cabin and then the bathrooms, Alice and Bill find no one around and they start to suspect it isn't a setup or a prank and is actually something serious, though Bill tries to keep Alice calm by suggesting otherwise. The two break into Steve's office and find the phone lines have been cut. They try to take Jack's car to town, but it won't start. With a 20 mile walk through a pitch black forest and the pouring rain out of the question, the two give up and decide to wait at the main lodge for Steve back.
Meanwhile, Steve finishes his meal at the local diner. Knowing they are new to the camp and not as skilled as he is, Steve decides to head back to Camp Crystal Lake to check up on them, instead of waiting out the storm in town. Partway down the road, Steve's jeep gets stuck in the mud and, because of the heavy load of supplies he's hauling, he can't get it out. A passing policeman offers him a ride back to camp, but gets a report of a serious accident in town and is forced to drop him off as close as he can. As Steve walks the rest of the way back, he is stopped by a flashlight at the Camp Crystal Lake sign. Apparently recognizing the person, Steve asks what they are doing out in this mess of a storm. The killer then stabs him with a knife.
Arriving back at the camp, the killer goes to the power generator cabin and disables it, forcing Bill to go out and investigate; he insists Alice stay in the cabin rather than follow. When Bill does not return, Alice becomes concerned again and heads out to the generator cabin to look for him. Not finding him in the small cabin, she closes the front door, and she finds his body pinned to the door by several arrows. Now alone, terrified and knowing that something is killing her friends, Alice flees back to the main cabin and tries to barricade herself in. After a few moments of silence, Brenda's corpse is hurled through a window.
Alice hears a vehicle outside of the cabin and, thinking it to be Steve, runs out to join him and escape. Instead she finds a middle-aged woman who introduces herself as Mrs. Voorhees (Betsy Palmer). Mrs. Voorhees explains that she is an old friend of the Christy's. Alice hysterically warns her away, but she insists on going inside to check after being told about the deaths. Mrs. Voorhees expresses horror and sadness at the sight of Brenda's body, and starts criticising Steve for trying to open the camp after all that had happened here. Calling the camp cursed, Mrs. Voorhees tells Alice that her son Jason died at the camp in 1957. Mrs. Voorhees goes on a tangent, describing how she was the camp's cook and how Jason, who wasn't a good swimmer, had drowned in the lake when the councilors left the children, and her Jason, unsupervised to go off and have sex. After telling Alice that June 13th, a Friday, is her son's birthday, she switches between talking to herself and shouting at Alice, accusing her personally of killing her son. Mrs. Voorhees pulls out a hunting knife, the same one used to kill several of Alice's friends. The class ring on her left hand removes all doubt that Mrs. Voorhees is the killer. A lengthy chase ensues, during which Alice flees her attacker and finds Annie's body in Mrs. Voorhees jeep, and Steve's body, hanging upside down outside.
Mrs. Voorhees heads back into the generator room to turn the power back on before continuing the chase. She corners Alice in a storage shed, where Alice finds a shotgun, but the ammunition drawer is chained and locked. Before Alice can load it, Mrs. Voorhees attacks her and slaps her around. Alice escapes and runs back to the main cabin, hiding behind a locked door in the pantry. Mrs. Voorhees breaks the door open and rushes in at Alice, brandishing a machete. Alice hits her on the side of the head with a frying pan, knocking her out. Alice sits by the lakeside, hoping that it is all over, but Mrs. Voorhees rushes out of the darkness at her with the machete. Narrowly avoiding the machete, Alice knocks it out of her hands with a paddle and the two wrestle by the lake. Besting her attacker, Alice grabs the machete and decapitates Mrs. Voorhees in one stroke. In shock, Alice gets in a canoe and hand paddles out to the middle of the lake, where she falls asleep.
Morning comes, and Alice is still asleep in the canoe. Police arrive and call out to her, and she awakens. As she sits up and contemplates her rescue, the decomposing "corpse" of Pamela's son, Jason (Ari Lehman), attacks Alice and pulls her, screaming hysterically, out of the canoe. As she is dragged underwater, she awakes in a hospital. When she asks about Jason, the police inform her that they never found any boy inside that lake. Alice then whispers, "Then he's still out there".
- Betsy Palmer as Mrs. Voorhees
- Adrienne King as Alice
- Jeannine Taylor as Marcie
- Robbi Morgan as Annie
- Kevin Bacon as Jack
- Harry Crosby as Bill
- Laurie Bartram as Brenda
- Mark Nelson as Ned
- Ron Millkie as Officer Dorf
- Walt Gorney as Crazy Ralph
- Willie Adams as Barry
- Debra S. Hayes as Claudette
- Dorothy Kobs as Trudy
- Sally Anne Golden as Sandy
- Mary Rocco as Operator
- Ken L. Parker as Doctor
- Ari Lehman as Jason
Make-up artist Tom Savini, famous for working with George A. Romero, did the special effects for this movie and Friday the 13th: The Final Chapter.