Two hunters, Sampson and his son Ainsley, are fishing in a swamp during a full moon. Ainsley says he has to use the restroom, and Sampson rows their boat to shore. While Ainsley is urinating, Sampson falls silent; Ainsley goes to see where he is and finds Sampson's mutilated body. He grabs his harpoon, only to be murdered by a monstrous being.
During a Mardi Gras celebration in downtown New Orleans, a group of friends, including Ben and his best friend Marcus, who have come to have some fun since Ben's girlfriend of eight years recently dumped him. Ben decides to go on a haunted swamp tour, and Marcus agrees to go with him. The two find that the tour is closed because the guide, Rev. Zombie, was sued. Rev. Zombie suggests that they try a place farther down the street, owned by the over-the-top, inexperienced tour guide Shawn. Marcus decides to leave but changes his mind upon seeing two topless girls: Misty, a ditzy porn star, and Jenna, a bossy, boastful, up-and-coming actress. Their sleazy director, Shapiro, is also there. Ben pays for himself and Marcus and Shawn leads them to his tour bus, where the other tourists, Mr. and Mrs. Permatteo, a Minnesota couple, and the quiet, hot-tempered Marybeth are waiting.
Ben tries to make friends with Marybeth, who rejects him, while Marcus takes a liking to Jenna. Shawn does not know what he is doing, which the others realize as they arrive at the swamp. Shapiro has Misty and Jenna strip down and film a scene for Bayou Beavers as everyone boards the boat, while a homeless swamp-dweller warns them away from the swamp. Shawn leads them through swamplands and past abandoned houses, including one where Victor Crowley, a deformed creature, lived. Shawn mentions "one night Victor's dad goes crazy and whacks him in the face with a hatchet" while looking at "ghost lights"; however, Mrs. Permatteo sees someone in the trees, and Shawn accidentally crashes into a rock, sinking the boat. To reach land, they must walk across a broken tree. Mr. Permatteo is bitten on the leg by an alligator, making him, Misty and Shapiro fall into the water. They reach shore and run to safety, while Mr. Permatteo bleeds profusely. They realize that Shawn is not a tour guide; he is just a college student looking for money. Marybeth takes out a gun she brought and informs them that her father and brother, Sampson and Ainsley, disappeared while fishing nearby, presumably at the hands of Victor Crowley. She then tells them the real story of Victor Crowley.
Long ago, presumably the 1940s-1960s, Crowley was a deformed boy who was kept hidden from the world by his father. One Halloween, a group of kids decided to scare Victor by throwing fireworks into his house, but the house was engulfed in flames. Victor's father tried to hack down the door with a hatchet to save Victor, but because Victor was pressed up against the other side of the door trying to get out, he hit him in the face with the hatchet, killing him. Victor's father died of a broken heart ten years later. Marybeth believes Victor roams the swamp as a vengeful spirit, killing anyone who enters.
Victor mostly kills people near his house, which they are standing in front of. Mrs. Permatteo becomes infuriated with how scared everyone is and decides to help her husband into the house. Victor emerges and kills the Permatteos. Marybeth shoots Victor, but only makes him fall. While running away, Shapiro is separated from the others and killed by Victor.
The others find Shapiro's body. Marybeth suggests they return to the Crowley house to get weapons, and all six of them go to the house. Jenna, Shawn, Marcus and Misty stand guard while Marybeth and Ben go into the shed to get weapons, but find Sampson and Ainsley's bodies instead. Ben comforts Marybeth, and they grab a shovel and a pitchfork, while the others are scared by noises in the bushes. Jenna is killed by Victor as Marybeth and Ben arrive with the weapons. Marybeth hits Victor with the shovel, making him fall and get stabbed with the pitchfork by Ben. Shawn reaches for the shovel but Victor grabs it first, chopping off Shawn's leg with it, and then decapitating him while the others flee.
The survivors decide to lure Victor back to his house and set him on fire with the gasoline tanks in the shed. They return to the house and Ben goes into the shed to retrieve a gasoline tank, while Misty stands guard and Marybeth and Marcus act as bait to lure Victor in. Marybeth and Marcus discover that Misty is missing, and her head and torso are thrown onto Ben by Victor. Ben finds a tank and throws it on Victor while Marybeth and Marcus set him on fire, but it begins to rain and the fire is extinguished.
The three begin running through a cemetery and find the gate locked; Ben is tackled by Victor who spits up blood in his face before he is dragged to safety. They start running away but Marcus is grabbed by Victor and killed. Victor grabs a gate pole and chases Ben and Marybeth, throwing it into Ben's foot. Marybeth bends the pole until it is pointed at Victor, who impales himself upon it. Ben and Marybeth board Sampson's boat and head out; Marybeth is snared by seaweed. She sees Ben's arm sticking into the water for her to grab, but is pulled up by Victor, who is holding a dying Ben's severed forearm. The film ends with Victor holding her screaming.