 
In the beginning of the film, there is archive footage of a police search of the Hewitt house. It is August 20th 1973. The two officers survey the house and desend into the basement, noting the fingernaill scratch marks, human blood and hair embedded into the walls. We are brought to August 18th 1973, where five young adults, Erin (Jessica Biel), Kemper (Eric Balfour), Morgan (Jonathan Tucker), Andy (Mike Vogel), and Pepper (Erica Leerhsen), are on their way to a Lynyrd Skynyrd concert after coming back from Mexico. As they drive through Texas, they see a distraught hitchhiker (Lauren German), who eventually gets in their van. After trying to speak to the hitchhiker, who speaks incoherently about a "bad man," and that she just wants to "go home", she shoots and kills herself with a .357 Magnum when she tells the group they are going the wrong way. The group tries to contact the police, then go to a store where a woman tells them the sheriff is at the mill. Instead of the sheriff, they find a little boy named Jedediah (David Dorfman) who tells them that the sheriff is drinking at home. Erin and Kemper go through the woods to find his house, leaving the other three at the mill with the boy. They come to a plantation house where Erin is allowed inside by the owner, an amputee named Monty, to phone for help. When Erin finishes, the old man asks her for help, using the opportunity to fondle her without her noticing. Kemper goes inside to look for Erin and is killed with a sledgehammer to the back by Thomas Hewitt aka Leatherface (Andrew Bryniarski) and drags his body into the basement.
Meanwhile, Sheriff Hoyt (R. Lee Ermey) arrives at the mill and disposes of the hitchhiker's body, wrapping her in cellophane and putting her in his trunk. Erin arrives and finds that Kemper is still missing. The group search the area, coming across a miniture junkyard of rusted old cars. They search quicker when Andy finds a full row of human teeth on the ground. Andy and Erin go back to the Monty's house, where Erin distracts him while Andy searches inside for Kemper. He looks around but only finds rotting meat and hanging from the ceiling. He yells and Monty realizes Andy is inside. He starts banging on the floor trying to intimidate Andy and Erin, suddenly Leatherface appears behind and attacks him with his chainsaw. Erin escapes and heads towards the woods. Leatherface chases Andy and saws his leg off. Leatherface carries him back into the house and drags him into the basement. We see that the fingernail scratches on the walls from the Police footage were made by Andy. Leatherface hangs his body from a meat hook and rubs salt on his leg stump, wrapping it in butcher paper.
Erin makes it to the mill and tries to escape in the van, but the sheriff shows up and, after finding marijuana, orders Erin, Morgan and Pepper to go out of the van. The sheriff gives Morgan the gun he took from the hitchhiker and tells Morgan to reenact how she killed herself. Morgan, scared and disturbed by the sheriff's demeanor, attempts to shoot the sheriff only to find the gun is unloaded. Sheriff Hoyt handcuffs Morgan and takes him to the Hewitt house. He tells someone over his radio that they haave two "plumpies" at the Crawford mill that need picking up. The sheriff tries to befriend Morgan asking him where he was heading. Morgan says a Sknyard concert. Sheriff Hoyt is surprised because now they have something in common. He suddenly smashes a whiskey bottle off Morgans face, and tells his that now they have something else in common, missing teeth. Meanwhile at the mill, Leatherface attacks the girls van. He climbs on the roof and begins to cut through it. Pepper runs, but is cut in half by Leatherface's chainsaw. When he turns around Erin sees that Leatherface is wearing Kemper's face over his own. Erin manages to escape and hides in a trailer with two women inside, who offer her tea and try to soothe her. They tell her that "sweet, innocent boy knows not to be playing around here. Hes such a nice boy, always keeps to himself because of his skin disease. Started when he was just a child". Suddenly a phone rings and after Erin questions them about why they lied she discovers they have kidnapped a child. However, the tea is drugged and she passes out when she tries to leave.
Erin wakes up at the Hewitt house surrounded by the Hewitt family: Leatherface, his mother Luda May, Sheriff Hoyt, Monty, and Jedediah. Luda May's excuse for her son Thomas's actions, was that her son was tormented by teenagers and that she felt no one cared for her family besides themselves. Erin is taken to the basement, where she finds Andy. She tries to help him off of the meat hook but when he sees he will land on the piano keys and alert Leatherface, he begs her to kill him, which she does. She finds Morgan, still handcuffed, and Jedediah leads them out of the house. Jedediah rejects Erin's plea to come with them and distracts Leatherface long enough for them to escape. Erin and Morgan find an abandoned house in the woods and barricade themselves inside. Leatherface breaks in and discovers Erin, but Morgan attacks Leatherface, causing him to drop his chainsaw. Morgan grabs him and wrestles him, but Leatherface is too strong and easily lifts Morgan upwards onto a chandelier before releasing him and Morgan gets tangled in the chandelier by his handcuffs. Leatherface picks up his chainsaw and slices up into Morgan's groin, killing him.
Erin runs out of the shack and escapes through the woods. Leatherface trips and cuts his leg while pursuing her. Erin finds a slaughterhouse and hides in a locker; Leatherface opens the locker across from hers and she attacks him with a meat cleaver, and chops off his right arm. Erin runs outside and flags down a trucker. She tells him she just wants to "go home" and panics when she sees he is going the wrong way .He stops to find help at the eatery. Erin sees Luda May and watches as Sheriff Hoyt arrives and talks to the trucker. Erin sees the Hewitt family with the kidnapped baby in a highchair. Erin sneaks the baby out of the eatery and hot-wires the sheriff's car before running him over repeatedly until he is dead. As they are driving along, Leatherface suddenly appears and slashes his chainsaw against the car, but Erin and the baby escape unharmed.
The police archive footage continues to play. The officers inspect the basement noting the hanging meat hooks when suddenly one of the officers is grabbed and severly beaten. A blurred figure viciously shakes the camera and the other police officer is heard screaming. The narrator states that " The crime scene was not properly secured by Travis County Police. Two investigating officers were fatally wounded that day. This is the only known image of Thomas Hewitt, the man they call Leatherface. The case today still remains open".