On a summer night, a young woman named Ginny Fields runs away from a pursuer through the forest and into a cabin. Inside, she finds the rotting head of an old woman sitting atop a sweater. She dons the sweater as her attacker breaks down the door, wielding a pickaxe and wearing a sack over his head. Ginny addresses him as “Jason,” and pretends to be his mother. Jason imagines his mother’s disembodied head speaking to him, ordering him to kneel. Just before Ginny chops off his head with a knife, he slices her leg open, and a young man pulls Jason away. The girl strikes Jason on the back of his neck, and he collapses. After the man leads Ginny out of the cabin, Jason crawls away. In the small town of Crystal Lake, a woman watches a television news report about eight people who were murdered on the local campgrounds. Ginny, the only survivor, has been taken to the hospital. A few minutes later, Jason appears outside the house and stabs the woman and her husband, Harold. One sunny afternoon, a group of suburban teenagers discuss their upcoming trip to the cabin of their female friend, Chris, when a boy named Shelly sneaks up on them with a mask and rubber knife. Shelly’s roommate, Andy, scolds him for behaving immaturely and encourages him to be himself to impress his date, Vera. When Vera joins them, Shelly apologizes for his appearance. Chris sees smoke emitting from her van, and they discover their two friends, Chuck and Chili, inside, smoking marijuana. As Chris drives, Debbie reveals that she is pregnant with Andy’s child. When they hear police sirens behind them, the group tries to hide the marijuana by eating it, but realize the officers are speeding past them toward Harold’s house. Chris nervously watches as paramedics remove two bodies on gurneys. The teens then encounter a sleeping man in the middle of the road, who shows them an eyeball that he found earlier that day. Jumping back in the van, the friends drive toward the cabin. Inside, a man named Rick grabs Chris and kisses her, but she asks him to slow down, since she has not seen him for many months. As Rick helps Chris lift hay into the barn loft, someone inside the house screams. Chris returns to find Shelly in the closet with a toy axe through his head, covered in blood makeup. Realizing the prank, Chris becomes upset and takes a walk with Deb, admitting that she is anxious after a terrible incident that occurred the previous summer. Meanwhile, Vera and Shelly borrow Rick’s car and go to the store, where they encounter three members of a motorcycle gang who attempt to steal Shelly’s wallet. When Shelly accidentally backs the car into their motorcycles, one of the bikers, Ali, shatters the car windshield. Upon seeing his wrecked car, Rick decides to leave, but Chris begs to accompany him. While their friends swim in the lake, the bikers arrive at the cabin and drain the gasoline from the group’s van. Inside the barn, a previously unseen killer stabs two of the bikers, Fox and Loco, with pitchforks, and chops off Ali’s arm. That night, sitting near a stream, Rick asks Chris why she returned to the camp, and she claims that she wanted to “prove something to herself.” Inside, Shelly admits to Vera that she has developed feelings for her, but she rejects him and steps outside. Meanwhile, Chris tells Rick about a night she was angry with her parents and ran into the woods; she was attacked by a “hideous-looking, almost inhuman” man, wielding a knife. She says the man dragged her body across the ground and she blacked out before waking up in her own bed, with no acknowledgement of the incident from her parents. After finishing her story, Rick’s car battery dies, forcing them to walk back to the cabin. While Chuck uses the bathroom, he believes he hears Shelly entering the barn. He and Chili investigate, but realize that Shelly is not the intruder. Meanwhile, Shelly hides under the dock and grabs Vera’s foot, causing her to become angry. He walks away and follows Chili and Chuck into the barn. When Vera realizes she still has Shelly’s wallet, she accidentally drops it into the pond and wades into the water to retrieve it. Jason appears, wearing a hockey mask, and shoots her through the eyeball with a harpoon. Inside the house, Debbie and Andy make love. Afterward, Jason murders Andy while Debbie takes a shower. Just as Debbie finds her lover’s body suspended from a ceiling rafter, the killer stabs her through the chest. Meanwhile, Chuck is murdered while attempting to fix an electrical outage in the cabin’s storage room. Shelly collapses before Chili in the kitchen, his throat sliced open, which Chili mistakes for another prank. As she realizes he is truly dead, Jason stabs her with a hot poker. When Rick and Chris return, the killer crushes Rick’s skull, popping his eyeball out of his head. Chris finds the bathtub full of bloody clothes and water, and discovers the bodies of one of the bikers outside. As she screams for Rick, Jason throws her boyfriend’s body through the window and chases her upstairs. Hiding in a closet, she discovers Deb’s body, pulls a knife from the corpse’s back, and stabs Jason in the leg. She uses a chair to break a bedroom window and attempts to jump out, but he grabs her jacket. The fabric rips, and she falls to the ground. Chris drives the van across a nearby bridge, where the vehicle runs out of gasoline and the back tires become stuck in the wooden planks. Unable to continue, she returns to the barn and hides in the loft. After striking Jason on the head with a shovel, she ties his neck with rope and hangs him. When she goes downstairs, however, Jason revives and lifts his mask, revealing that he is the same disfigured man who attacked her the previous summer. Ali jumps out from the darkness and attempts to kill Jason, but Jason stabs him. Chris plunges an axe into Jason’s forehead, and he collapses. The girl gets into a canoe and falls asleep on the lake. When she awakens the next morning, she sees Jason, his face bloodied, in the upstairs window of the house. She turns again and realizes the man is gone, but the corpse of Jason’s mother springs from the pond and drags Chris under the water. Later, three police officers retrieve Chris from the cabin, still alive. They believe that she imagined the lady in the lake, since they find Jason’s dead body lying in the barn.