A group of friends—siblings Oscar and Karen, Beth, and Beth’s marine infantry boyfriend Randy, along with Randy’s sister Emily and her ex-Navy SEAL boyfriend Niles—find themselves traveling through the backwoods town of Fort Collins, Louisiana. They stop at a gas station run by a man named Chopper, where Oscar discovers a shrine dedicated to a local legend known as Lockjaw. The locals point them toward Grimley, a roadside attraction and urban legend built by a reclusive local named Grimley. Oscar and Karen persuade the others to explore it, hoping for a thrill and a story to tell.
Oscar wastes no time sharing the legend of Lockjaw as they push deeper into the mystery. Long ago, Grimley Boutine and his sister Caroline were the last of their clan, bound by a forbidden, incestuous relationship. Caroline became pregnant with Grimley’s child, and just before their wedding, an albino alligator dragged Caroline into the swamp. Grimley, desperate to save her, hunted the gator, killed it with his bare hands, and, in a horrifying turn, consumed the flesh of the gator, then his sister, and eventually every scrap of flesh in the cave. The ritual of cannibalism and rage twisted him, transforming Grimley into a fearsome half-man, half-alligator—the legend of Lockjaw that the town would rather forget. Not everyone believes the tale, but the aura of the story lingers as they reach the area around Grimley’s house.
They set up camp near the Grimley residence, unaware that they are being watched. The night unfolds with a mix of drinking and bravado, but danger seeps in from the edges of the story. Earlier, a shop patron named Grover was slaughtered by an unseen creature along the riverbank after ignoring warnings to stay away from Grimley’s domain. Randy leaves the group to fetch more beer, returning just in time to interrupt Karen as she and a drunken Beth are about to become intimate. Oscar, in a more troubling turn, secretly photographs Niles and Emily sharing a kiss and engaging in sexual activity. When Karen discovers him, she engages with Oscar in a moment that hints at a complicated family dynamic, as it becomes clear that Karen and Oscar share a disturbing secret: they are also tied to Chopper as his children. Chopper—subservient to Lockjaw—sets his sights on Karen and takes her away, while Randy, witnessing the chaos, encounters Lockjaw again and runs off into the woods. Oscar falls into a daze after accusing Randy of assault, while Niles separates from Emily to seek out Randy. What follows is a deadly chain of encounters: Randy and Niles cross paths with Lockjaw, stumble toward a highway they believe is far from where they started, and are forced to confront the danger closing in around them. A shop worker stops them at gunpoint, but Niles manages to kill him, only to be confronted by the murderous presence of Lockjaw, who kills Randy in a brutal encounter.
Beth awakens to find her tent moved into a dark cave, where she screams at the sight of Lockjaw feasting on a victim. Meanwhile, Karen is prepared as a sacrificial offering to Lockjaw; her father severs her feet to lure the beast from the depths, a grim act meant to appease the creature. The ritual seems to have a familiar turn when Lockjaw appears to recognize Karen by a necklace she wears—the same talisman Gabrielle’s necklace that Chopper had placed around her neck, linking her to the cult’s history. Niles finds Karen dead in the cabin and is attacked by a disturbed Oscar; he defends himself with Oscar’s machete and moves on.
Niles then makes his way to Lockjaw’s cavern in an effort to save Emily, but both are captured by the cult. Lockjaw throws Niles into the river, while Chopper tells Emily that Lockjaw has chosen her as the next bride. Niles follows the others to a ritual gathering in which Grimley’s plan is to impregnate Emily. In a fierce confrontation, Niles fights Lockjaw and manages to knock him into a sinkhole. He frees Emily, but Lockjaw drags her back into the depths, pulling both of them down as he disappears into the darkness. The next morning, Emily and Niles emerge from the sinkhole with Lockjaw’s jaw as a chilling trophy, and they drive away together, leaving the cult behind.
Some time later, Chopper appears at the refurbished Grimley cabin where a celebratory gathering is underway. Beth is revealed to be alive, but she carries a mutating baby, a stark reminder of the twisted rituals that surrounded Lockjaw and Grimley. The ending leaves a sense that the nightmare continues, with the survivors carrying the echoes of the legend as they move forward.
