The film begins with a man running for his life through the forest. As he looks around, something comes up from behind him, throwing him up into the air. The man screams as something begins eating him, and the camera turns to a pair of dog tags.
John Hickman and his girlfriend Brooks are San Francisco residents who invite their friends, self-proclaimed tough guy Ben, his close friend Wayne, chef Quincy and his dog Wolfgang, to a weekend of hunting and drinking near John's uncle's remote cabin. Ben and Wayne can't stand Brooks, and the feeling is mutual — they spend much of the trip getting on each other's nerves. En route, they stop at a gas station/general store for directions and encounter a van of hippie women and their leader, the Hippie Stranger, who live in a commune in the woods, presumably raising emus for meat. From the store owner, they learn about a local legend called "The Ripper," a legendary killer hog which supposedly weighs several thousand pounds. After obtaining supplies and directions, they make their way to the cabin, passing through a hillbilly homestead belonging to the Tibbs clan. One young boy is perched in a tree, and drops a dead animal carcass on the hood of their car as they pass underneath. When they get to John's uncle's cabin, they find it vandalized and uninhabitable, though John maintains the rednecks down the road weren't responsible. The group pitches their tents and camp outside.
The next morning, they encounter methamphetamine-addicted hillbilly brothers Jake and Ricky Tibbs, cousins of John's, who are interested in joining them on a wild hog hunt. An old feud still exists between John and Ricky, who is a Gulf War veteran showing signs of mental illness. Quincy, who is eager to get to know them, is obviously inexperienced in any sort of outdoor activities, and Ricky accuses Wolfgang of being a "pet" not a "dog". When Jake sets up some targets to see how well the others can shoot, boastful Ben makes a fool of himself, and Wayne is only able to hit the target a couple of times. Brooks outshoots both men, impressing Tibbs.
As the group travels through the woods, they encounter an area called the Big Wallow and, using a piglet call as a lure, manage to attract several pigs. One of them rams into Wayne's leg, incapacitating him with a compound fracture at the kneecap. Wolfgang goes charging after the boars while Brooks shoots one of them. Ricky calls Jake to come look at something disturbing he's observed while skinning the hog they killed. Though adult-sized, it has no protective armor over its shoulders — it is not a full grown animal as they had thought, but a piglet. Quincy reappears - while looking Wolfgang, he encountered a large crop of marijuana plants and now leads the others to it, leaving Brooks with Wayne.
John objects to Jake and Ricky taking the plants for profit, as they are growing on his property and he wants no part of it. There is also a strange sign posted near the plants, which leads John to think that the hippies that he thought were raising emus are actually growing pot instead. During the ensuing argument, Ricky snaps, and holds John at bay with a crossbow. John and Jake are trying to gain control of the situation, when Ben arrives on the scene, thinks Ricky is about to kill John, and shoots him. Jake flees to tell his clan, and the others return to Wayne and Brooks. Quincy and Ben start making their way back to the cabin while Brooks and John leave Wayne to find something to make a stretcher with so they can carry him out of there. Shortly after their departure, Wayne is attacked by something, and manages to fire off a single round. Brooks and John circle back and find him missing, as well as Ricky's body.
Meanwhile, Ben and Quincy make their way back to the cabin and find Wolfgang's mutilated body, determining that he was killed by the Tibbs clan. Ricky and Jake's clan appear, Ben manages to kill his pursuer and escape, but Quincy is knocked out of the vehicle he was attempting to escape in, and is executed by a single gunshot to the back of the head. At the same time, John and Brooks run into the mysterious Hippie Stranger as they hide in the forest; he is carrying a cattle prod, and tells them that he is looking for an escaped animal, and that they can contact the police from his commune. He helps them beat off an attack by the Tibbs clan, and several hillbillies are killed. In the meantime, Ben has found the commune, where he is given drugs by several women, and led into an enormous, muddy pen. He encounters a dying Wayne, who says that something has been eating him. Ben turns as something approaches him from behind, and screams.
The remaining Tibbs clan members reach the woods around the commune. They are stalked and killed, one by one, by the murderous hippie women — all except one man, who is seized by something else. Brooks and John arrive at the commune with the Hippie Stranger. When John questions why Ben's equipment is there, but not Ben himself, they force him into a cell while the leader takes Brooks out into the pen. The legendary Ripper is revealed, with the remains of one of the redneck clan in his mouth. Meanwhile, Jake makes his way into the commune, and is confronted by some of the women. He shoots a couple of them, and forces one of the women to let him into John's cell. As Jake sees the Ripper out in the pen and freezes in shock, the hippie he brought with him attacks, stabbing him in the eye before John kills her. Jake dies from his wounds while the Hippie Stranger prepares to sacrifice Brooks to the boar, whom he and his followers have been worshiping. Brooks gets a hold of the cattle prod and pokes him with it, causing him to cry out, attracting the Ripper's attention. The creature eviscerates him, and Brooks remains quiet as John forces his way from the cell. Using a crossbow, he fires an arrow up under the boar's jaw, killing it. As Brooks and John make their escape, they come face to face with the feral boy who was sitting in a tree at the beginning of the movie.
