A group of friends from New Jersey, including Jen Shaw, her boyfriend Darius, and couples Adam and Milla along with Gary and Luis, embark on a journey to a quaint town in rural Virginia with plans to hike the Appalachian Trail. Upon arrival, they meet several local residents, one of whom is Nate, who caution them about the dangers of straying from the marked paths. Jen also encounters a mysterious woman named Edith and a young mute girl named Ruthie, adding an eerie layer to their trip.
As they delve deeper into their hike, a tragic accident occurs: a rolling tree trunk crushes Gary, taking his life and leaving the group in a state of confusion and grief. That evening, they set up camp, only to find the following day that Milla has vanished along with their cellphones. In their search for Milla, the group stumbles upon an unsettling plaque from 1859, commemorating a group of settlers known as the "Foundation," who had foreseen the impending end of the United States.
While searching, Adam inadvertently finds himself ensnared in a trap. After being rescued, a struggle ensues in which Adam kills one of two men dressed in primitive attire and animal skulls. Shortly after, Milla reappears, revealing she had been hiding from the men. However, their escape is thwarted when Milla falls into a pit, impaled on jagged tree branches, and Adam, in a moment of panic, abandons her as she is shot by an arrow from one of the masked men. The remaining friends—Jen, Adam, Darius, and Luis—are captured and taken to the Foundation’s primitive settlement.
Before their captors, led by the cruel Venable, they are charged with murder. Jen recognizes Edith and Ruthie from their encounter earlier. Venable finds Adam guilty, sentencing him to death, while Jen, Darius, and Luis are accused of lying and sentenced to a fate described ominously as "darkness." Adam meets a gruesome end at Venable's hands; Luis’ desperate escape attempt ends with him being brutally blinded. In a moment of desperation, Jen pleads for mercy from Venable, claiming she and Darius could be of use, which leads to her being oddly welcomed into the cult.
Weeks later, Jen's father, Scott Shaw, comes searching for her and is aided by a local motel owner. He hires a tracker to navigate through the perilous woods, only to find himself in danger as the tracker and his son fall victim to traps set by the Foundation. When Scott finally locates the cult's settlement, he is immediately surrounded and captured. In a twist of fate, Jen, now seemingly brainwashed and wedded to Venable, shoots her father with an arrow, but reveals later that it was an act to spare him from suspicion.
As Jen and Scott attempt to escape, they encounter Darius, who chooses to remain behind. Jen receives assistance from Ruthie in their flight, and the group survives clashes with the cult, culminating in the death of several cult members, including Edith. When they are ambushed by armed townsfolk, hope reignites as they collaborate to fend off the attackers. Ultimately, Jen's determined spirit leads her and her father to safety, but at a cost, as they are forced to confront the horrific remnants of their ordeal.
Months later, while adjusting back into their normal lives, Jen visits her stepmother only to find Venable and Ruthie at her home. During a confrontation, it's revealed that Jen, pregnant with Venable’s child, is coerced into returning to the Foundation, but only under the stipulation that he stays away from her family. In a final act of defiance, Jen, along with Ruthie, embarks on a chaotic escape in an RV with Venable and several cultists. The vehicle loses control, leading to a violent crash. In the chaos, Jen avenges herself by stabbing Venable and killing another cultist in her path before seeking solace with Ruthie as they make their way back to her family home, forever changed by their harrowing experiences.
