In the summer of 1957, at a small-town summer camp named Crystal Lake, a young boy named Jason Voorhees drowned in Crystal Lake because the counselors were too busy exploring each other than watching Jason. Jason went out too far into the lake and did not know how to swim. He drowned, calling for his mother as he went under. A year later, the camp is re-opened, when two camp counselors, Barry and Claudette, allegedly the same two who let Jason drown, snuck away from a group rendition of "Tom Dooley," for another attempt at enhancing their pleasure. However, someone is waiting for them and brutally murders them with a knife. Over the course of the next 20 years, several attempts to re-open the camp were stalled for various reasons, which included bad water in 1962 and a series of fires. Finally, in 1978, Steve Christy, son of the original camp's owners, decided once and for all to open the camp and forget about its storied past. After spending more than $25,000 and over a year at the camp fixing it up, final preparations were being made, and all the counselors were arriving, except one. Annie, who was to be the camp cook, came to town to try to hitch a ride for the 20-mile trek to camp. After being warned by the townspeople and town loony Crazy Ralph to stay away from "Camp Blood," she hitched a ride with a local out to the crossroads, halfway to camp. She then got halfway down the crossroads when a mysterious jeep picked her up. When the turn for camp came, the driver deliberately drove past and drove in the wrong direction. Annie, noticing the error, bails out. But the driver chases her down into the woods and slits her throat with a hunting knife. Meanwhile, Steve Christy leaves camp to run errands in town and the counselors, Bill, Alice, Brenda, Jack, Marcie and Ned continue to work. After some typical teenage antics and continued warnings from Crazy Ralph and the local policeman, the counselors prepare to close up for the night in lieu of a bad storm that is threatening the mid-summer sky. Ned, who notices Jack and Marcie "getting close," turns to head to his cabin, when he notices something in the darkness. He goes into the cabin to check it out and never comes out. As the storm begins, Jack and Marcie shack up with each other for the night, and Bill, Alice and Brenda decide to play an erotic game of strip monopoly. When Jack and Marcie make love, a flash of lightning reveals the horror that lies above them-- Ned's body--with his throat slit. After their rendez-vous, Marcie leaves to go to the bathroom cabin and Jack waits for her to come back to keep him warm. Jack then lights up a joint to pass the time when Ned's blood drips down on him from the top bunk. Before he can react, Jack gets an arrow from the archery range through his neck from the unseen assailant under the bed. At the bathroom cabin, Marcie is relieving herself when she hears a noise that she thinks is Jack coming to play a prank on her. She heads toward the showers and moves the curtain, but nothing is there. When she turns around, however, the killer attacks her and annihilates her with a deadly axe swing to the face. In the meantime, Brenda, Bill and Alice's game of strip monopoly is just getting interesting when the door blows open in the storm, causing Brenda to remember leaving her windows open in her cabin. She leaves and Bill and Alice stay to clean up. Back in town, Steve Christy finishes up his dinner at a local diner and decides to head back to camp. Halfway there, his jeep stalls and a policeman gives him a lift. Once Brenda gets settled in her cabin, she hears a child's pleas for help in the woods. She goes into the woods to investigate and winds up in the archery range. Then all of a sudden, the lights are turned on, revealing that Brenda is standing directly in front of one of the targets..... At the same time, Alice notices the lights being on and tells Bill, who leads their investigation. In Brenda's cabin, they find a bloody axe. Alice wants to leave, but Bill persists, and they decide to go call for help. The phone lines are cut and so is the power to their truck, which won't start. Alice again wants to hike out of the camp, but Bill convinces her that all is well and they decide to stay. The officer giving Steve a ride is en route, when an emergency call comes in to the officer and he is forced to drop Steve off short of the camp. Steve walks the rest of the way, and when he arrives, he is blinded by a light. Steve, who at first had no clue what was going on, then recognizes who has the light. But it's too late. Steve falls victim to a knife in the stomach. The power is then cut to the camp and Bill goes to check the generator while Alice decides to get some sleep. Bill checks the generator and all appears well. Alice then wakes up a short time later and goes to look for Bill. Instead, what she finds is Bill pinned to the generator door with arrows. Alice goes berserk and locks herself in her cabin. But then, as Alice stands by a window, the body of Brenda is thrown through the window, sending Alice frantically running out of the cabin, and right toward an oncoming jeep. The jeep stops and out comes Mrs. Pamela Voorhees, who identifies herself as "an old friend of the Christy's." Alice thinks that Mrs. Voorhees is there to help, when in fact, it is Mrs. Voorhees who is the killer. She has been responsible for all the problems over the years with the camp ever since her son Jason drowned in 1957. So Mrs. Voorhees tells Alice that, "I couldn't let them open this place again, could I?" and all hell breaks loose. Alice manages to escape the clutches of Mrs. Voorhees and run off into the woods to hide, with Mrs. Voorhees not far behind.....