Plot
Clover, her ex-boyfriend Max, her friends Nina and Megan, and Nina's boyfriend, Abe, are retracing the steps of Clover's missing sister, Melanie. The group stops by a gas station from which Melanie had previously sent a message, and Clover meets the station attendant, Hill. He claims that people tend to go missing near Glore Valley, a mining town. They head there, but heavy rainfall forces them to seek shelter at a visitor center. There, Abe finds a wall filled with posters of missing persons, including Melanie. Nina signs the center's guestbook. Downstairs, the group finds another house underneath. A masked assailant kills Abe in the poster room, then kills Nina, Max, Megan, and Clover as they try to hide, flee, and attack him.
They awaken on the first night with a new, additional guestbook signature and their own missing persons posters on the board. They realize that the night is repeating, indicated by an hourglass in the main room. Megan is possessed and killed by a supernatural force that drags Clover into a dilapidated house across from the center, where she meets an elderly Glore Valley resident who says she can "survive the night or become part of it", then gasses her before disintegrating. Max tries to convince Abe and Nina to rescue Clover, but they try to escape instead. They flee in the car, but after seeing a giant creature in the woods, they turn back and are again killed by the assailant. Max goes alone and finds Clover, now possessed, and she immediately kills him before being run over by the masked assailant.
The night begins anew as the group realizes they are in a time loop with only thirteen deaths before the loop ends. They barricade themselves in the bathroom and drink the tap water, which causes them to explode. Before Clover dies, she sees Hill, who tells her that they cannot wait out the night. Starting again, the group finds a recording of Hill studying a man trapped inside a room. The man goes insane over the course of thirteen nights, ultimately turning into a wendigo. Clover contacts Hill through a radio, who claims that they can escape if one person permanently dies. He tells Clover to meet him in the woods alone, and that he might let her see Melanie. An argument arises between the group. Nina, angered by Abe's attempt to abandon them, impales him with a pickaxe. While Clover, Max, and Megan explore the woods, Abe and Nina are murdered again. Max and Megan are attacked by a wendigo in the woods, and Megan dies. Clover and Max find Melanie, who has turned into a wendigo herself. Heartbroken, Clover tells Max to kill her so they can learn more; he slits her throat and drinks the water to explode.
The next night, the group discovers that Glore Valley sank into the ground after a mining disaster, killing hundreds, and that Hill was brought in to act as a therapist to the survivors. The group awakens on their thirteenth night with no memory of the last several loops, their bodies starting to deteriorate into wendigos. Abe reviews footage on his phone showing that they tried to find Hill over several nights, but were repeatedly slaughtered by various creatures. They realize Megan is missing and find that she survived a night and has followed Hill into the tunnels. Ready to confront Hill, the group follows Megan's trail, fending off wendigos. Clover splits from the others and is forced to kill Melanie. She arrives at a sanatorium, where Megan is trapped with a wendigo. Clover confronts Hill, who reveals he is running experiments, and the creatures they faced are manifestations of Clover's depression and fears. Clover moves Hill's coffee under the water dripping from a ceiling pipe, and he explodes after drinking from the mug. She frees Megan as the others kill the masked assailant. The group flees through the tunnels and escape as the hourglass runs out and the sun rises, ending the time loop. After they drive away, the surveillance system in Hill's office changes to a snowy cabin where a car pulls up, with Hill heard whistling.
