A prologue recaps the ending of the previous story, beginning with sole-surviving Alice Hardy's (Adrienne King) flashback nightmare, in which she recalls encountering schizophrenic mother Mrs. Voorhees (Betsy Palmer). The camp's ex-cook was seeking homicidal revenge for the tragic and accidental drowning death of her young son Jason Voorhees at Camp Crystal Lake in 1957.
Two months later, Alice relives the horror of that night through a dream, when she decapitated Mrs. Voorhees with a machete, and is attacked in a canoe on the lake by the rotting decomposed corpse of Jason. She is told by a police officer that she alone had been pulled from the lake - culminating with her final words in the original story: "Then he's still there." After she wakes up from the dream, she talks on the phone to her mother, telling her that she is struggling to put her life back together.
Later, she takes a shower and decides to boil the kettle. The shower scene involves a few odd occurences - a hang-up phone call, a banging noise, and a screeching cat that leaps through her kitchen window. When she opens the fridge, she finds Mrs Voorhees' severed head.
While screaming, an ice pick is thrusted through her temple by an unknown killer, whose dirty hand removes the whistling tea kettle from the hot stove burner.
Five years later, a group of young adults have come to Crystal Lake to attend a counselor training center that has been set up near the now-condemned Camp Crystal Lake. The prospective camp counselors are dim-witted Jeff (Bill Randolph), his girlfriend Sandra Dier (Marta Kober), and their friend Ted (Stu Charno). Jeff and Sandra drive into a rural town, and from a payphone, call their friend Ted for directions. The doomsayer Crazy Ralph (Walt Gorney) from the first story approaches them.
Ralph tells the counselors to turn back, as he tried to warn the young counselors five years ago. They didn't believe him and he warns the new counselors they are all doomed. But they ignore his warning.
Jeff's illegally-parked truck is being towed away and they run after it as it is taken away by Max (Cliff Cudney), the gas station owner, not realizing that it was a prank orchestrated by their nerdy friend Ted who was around the corner. They finally retrieve their truck and continue their journey to the camp.
A large group of young adults are converging on the area, for a training session in a course called Senior Camp Counselor Course, led by Paul Holt (John Furey). The two-week training is to be held near the notorious Camp Crystal Lake (nicknamed "Camp Blood") at a new counselor training center called Packanack Lodge, in the Lake Region. From deep woods foliage, the trio are spied upon by an unknown individual, when they remove a large tree limb blocking the road, and find a broken down sign for Camp Crystal Lake lying nearby.
As the trainees assemble for the first time, a number of them are introduced by Paul, including: Terry (Kirsten Baker), Vickie (Lauren-Marie Taylor), Scott (Russell Todd), and Mark (Tom McBride). Mark, now bound to a wheelchair, had been in a motorcycle accident which left him with paralyzed legs. They are told that the course would be back to basics - survival, first aid, boating, archery, rifle range, etc.
Ginny (Amy Steel), Paul's girlfriend, arrives late, in her broken-down Volkswagon and attends the meeting as well. Ginny is Paul's assistant and a child psychology major. Paul explains how camp counseling is a serious job, and he unwittingly cautions the counselors about safety regarding axes, knives, lanterns, saws, they can all be trouble.
Their misuse is the main cause of camp accidents. He also reminds them that the main danger in the area is bears, therefore, no food fights. He recommendeds they change often because food odors cling to clothing. He warns the women not to use perfume and keep clean during their menstrual cycle.
One night, around a campfire, Paul tells the people about how Jason Voorhees drowned in the same lake which their training area also bounds. His mother was found to be the infamous murderer of Camp Blood and that Alice survived only to disappear shortly thereafter. Vanished. Blood was everywhere. No one knows what happened to her. Jason's body was never recovered from the lake after he drowned.
Some of the local residents believe Jason is still alive and viciously protects the area around Crystal Lake. Now a demented creature, he survives in the wilderness, stalking and stealing what he needs. Living off wild animals and vegetation. Legend has it that Jason saw his mother beheaded that night. And that he took his revenge. A revenge that he'll continue to seek if anyone ever enters his wilderness again.
And it's Paul's group that is the first to return to the area. When the counselors seem into the story, they are shocked by a mask-wearing man with a spear, but it only turns out to be the prankster Ted in a monster mask. As they express relieved laughter, Paul tells the crowd that the story is ancient history. Jason drowned. Mrs. Voorhees was killed. And Camp Crystal Lake is off-limits.
Later in the lodge building, the counselors entertain themselves by arm-wrestling, electronic video game-boy play, chess, or flirtatious getting-to-know-you talk. Sandra tells her boyfriend Jeff that she is intrigued by Camp Blood and has to see it.
As Ginny prepares for bed in her cabin, the shadow of Crazy Ralph crosses the entrance, just before Paul joins her for smooching-fraternizing.
Crazy Ralph watches them kissing through the front screen door, standing behind a tree. Suddenly, Ralph is killed by a barbed wire garotte around his neck.
The next day, the group of counselors engage in fun and games-training exercises (jogging, hiking a half-mile trail through the woods, etc.). Pony-tailed camp fitness director Ginny senses a presence watching them. During a hot-dog BBQ lunch, Terry leaves the group to look for her shaggy pet dog, Muffin.
The others have an afternoon swim break in the lake. Jeff and Sandra sneak away to the strictly off-limits Camp Crystal Lake, which is now in disrepair. They find the mangled remains of an unrecognizable dog, conjecturing it was the work of wild animals, and later decide not to tell Terry - fearing it was her dog, Muffin.
As they are about to go into one of the cabins, a man wearing muddy workboots and heavily-soiled jeans notices them. Local deputy Winslow (Jack Marks) appears and confronts them for trespassing.
The deputy returns the two counselors to camp. He sternly warns Paul that the nearby property is condemned and that the next group of trespassers will be jailed. Winslow states that things have been quiet for five years and that's the way he wants to keep it. Paul recommends only a light punishment.
However, when driving away, the deputy sees a mysterious individual dart out in front of his squad car, and is running in the direction of Camp Crystal Lake. Winslow chases the masked man on foot, only to lose him.
The deputy discovers a dilapidated, boarded-up ramshackle cabin with tarps on its roof, he enters the makeshift wooden building. Inside are pieces of broken-down furniture and rotting wood. He opens a door to an inner room and sees a horrifying sight (not shown to the viewer). Suddenly a claw hammer slams into the back of his head.
After dinner and getting to know one another, the majority of the trainees leave the campsite to party in town for the evening with the exception of a few. Jeff and Sandra are not allowed to go as part of their punishment. Terry chooses not to go to continue searching for her dog Muffin. Scott decides to remain at the camp (presumably to get to know Terry better). Mark chooses not to go so that the party would not have to deal with a drunk in a wheelchair. Vickie prefers to stay and talk to Mark. Terry announces she is taking a walk - and is followed by an unknown shadow.
At the lakeside, Terry strips down and goes skinny-dipping near the dock. As she swims, someone steals her clothes. She exits the lake and it is soon revealed to be Scott who stole her clothes. As they playfully fight, she demands her clothing back. Scott runs off and right into a noose snare-trap that swings him upside-down by a rope.
After teasing Scott a bit, Terry goes to look for something to cut him down with. While she is looking, Scott's throat is cut by the assailant, using a panga machete. When Terry returns, she thinks Scott is playing a game, but noticing his bloody neck, finds him dead. She screams, turns, and becomes the killer's next victim (killed off-screen).