Two men are hunting in a forest and come across an abandoned church. They go in to explore, and one of them receives a machete to the groin by a laughing man wearing a checkered jacket, while the other, Ty, runs away screaming. Next, we see park ranger, Roy McLean (George Kennedy) at his home, followed by a van of five teenagers going camping, but becoming lost. McLean warns them not to keep going the way they're headed, but they ignore him. The five are: Warren (Gregg Henry) the blonde, body builder; his girlfriend Constance (Deborah Benson), the shy, blonde girl; Jonathon (Chris Lemmon), the goofy, horny partygoer; his provocative girlfriend, Megan (Jamie Rose); and the nerdy camera operator, Daniel (Ralph Seymour). On their way to the campsite, they almost hit a frantic, dirty Ty who tells them to drive away, but they do not listen, and he runs into the woods. They finally find a campsite and begin to set up, drinking beer, eating, and listening to music, not paying attention to anything around them. When night falls they go to sleep, all the while being watched by something in the woods. The next morning, they eat breakfast and go to the waterfall, where they see a young girl named Merry Logan (Kati Powell) who runs off into the woods. Meanwhile, Megan and Jonathon have gone skinnydipping in the lake, not knowing someone is under the water with them. Megan does not realize that Jonathon has got out of the water, and feels hands touching her. She assumes it's Jonathon, until she sees him on shore, upon which she panics and swims to safety.When the group splits up to go exploring, Jonathon spots Merry and chases her, asking what her name is and telling her he will not hurt her. She thinks this is a game and runs out into a clearing where she sees something horrible, backing up towards the trees. Jonathon figures it's the roped passageway over the river ahead, and begins to go across, but Merry runs and he gives chase, only to be hit in the hand with a machete by a deformed, giggling man in a checkered shirt. Jonathon runs to the other side, only to have the rope break, almost plunging him to his death in the rapids below. As he begins to climb up, he is greeted by the same man, who shoves him off to his death with his boot. Megan and Daniel have gone off to takes pictures of the woods and come across the church and a graveyard. Daniel breaks his glasses and sees a figure coming through the woods, and thinks it's Jonathon and tells Megan, who decides to make it look like they're making out. Daniel sees the figure approach, and upon realizing it's not Jonathon, pushes Megan out of the way and is stabbed through the stomach with the machete. Megan sees the checkered shirt killer and runs into the church, where she sees him outside picking up Daniel's camera. She turns around and is greeted by the same man, and realizes that they're identical twins. He begins to chop her with the machete as the other takes pictures through the window. Meanwhile, Warren and Constance have met back at camp, but cannot find anyone else, until they spot Jonathon's body floating in the river, and pull him out. They go to find the others but cannot find any trace of them as night approaches, so they go back to get the keys from Jonathon's body which has disappeared. Ty finally meets Roy and tells him all about the killer twins at the church, and Roy goes out on his horse to find the teens, and comes across Merry's family, who consist of a crazy father, and silent sister/mother. They tell him that the twins were actually theirs and that their mother died after having them, so he mated with his daughter and had Merry. Warren goes to find Jonathon's body to get the car keys, and leaves Constance at the campfire, where she is attacked by one of the twins who chases her up a tree. Warren finds Jonathon's body along with Daniel's who is wearing sunglasses and gets the keys, running back to camp with the ranger. The twin cuts down the tree Constance is in, and is about to kill her when Roy shoots him in the chest, killing him, and he tells the couple to go pack their things. They go back to camp, as Merry runs through the woods to find them. At camp, the other twin stabs Warren and tries to kill Constance, who instead rams her fist down his throat, choking and killing him. Then she stands up, and makes the same noises as them, noting that she may have gone insane, as Warren questions her and Merry watches from the trees. The final shot shows the sunset view of the forest from the beginning.