Five high school friends hike up Lonely Peak for a final weekend together before they scatter after graduation. They are headed to a cabin owned by one member's family to play the last session of a tabletop role-playing game they have shared for three years. In the game, set in a fictional city called Gonfalon, they play inquisitors who solve magical murder mysteries. Ever, the group's game master who supports a younger sister and a father while living in poverty, designed the world and its stories. The other players are Finn, a trans boy who uses forearm crutches and lives with chronic arthritis pain; Liva, the wealthy daughter of an insurance executive whose family owns the cabin; Maddy, an autistic former lacrosse star whose career ended in a car accident; and Carter, an ambitious boy from a family that aspires to wealth but falls short. A sixth member, Liva's ex-boyfriend Zac, left the group months earlier after accusing Liva of treating her friends as projects to control.
The group is already fractured. Months before, Finn started a fight with bullies who insulted Ever and was badly beaten. He saw Liva nearby and expected her help, but she watched and did nothing. The betrayal destroyed their friendship and sent the group into an uncomfortable hiatus. Finn has come only because of his unspoken love for Ever, and he admits to himself that part of him wants to break the group apart further.
The hike foreshadows trouble. The path is blocked by boulders from a recent storm, and Finn refuses help climbing over them, nearly falling before Liva catches him. Carter mentions ghost stories about the mountain: tales of a serial killer whose victims heard a music box melody before dying. At the cabin, a modern structure with reinforced doors and automated locks, Ever has decorated the living room to resemble Gonfalon. The five change into costumes and begin to play.
Ever introduces the mystery of a murdered councilwoman found inside an arcane circle, a magical ritual pattern drawn on the floor. The players fall into their roles, but strange events intrude. The electric fireplace roars to violent life the moment Maddy solves a puzzle box. Maddy freezes, triggered by memories of her car catching fire after her accident. Liva cuts the power, and the group trades blame in the darkness. When the game resumes, Liva's character sacrifices herself to save Finn's character, and Ever rolls an astronomically unlikely lethal result. Shaken by the loss, Liva leaves the room.
She does not come back. A scream tears through the cabin. The group discovers Liva's bedroom empty, the window wide open. On the sill sits a wooden coyote figurine beside what appears to be a bloody, severed finger bearing nail art of the Gonfalon symbol. A note beneath reads "LIAR" (113). Outside, they find blood on the grass and torn pieces of Liva's costume. From the window, Ever spots bloody handprints on the cabin wall leading not away but back up toward the window.
The power cuts out, and the group's phones have been stolen from the pantry where Ever stored them. On the porch, Maddy is in a dissociative state, murmuring that Carter went back inside. The three search the darkened cabin and find Carter's body in his bed, eyes wide, mouth frozen in a silent scream. He is arranged like the murdered councilwoman from the game, surrounded by an arcane circle drawn in coins. A note pinned to his chest reads "THIEF" (151). His ring finger has been severed and replaced with a wooden rat carving.
The front door slams as automated locks engage. Finn touches the electrified doorknob and is thrown backward with a severe burn; a ward, a magical barrier symbol, has been drawn around the door. They pry it open using Finn's crutches as insulated levers. Maddy dives through first and holds the door from outside while Finn escapes. As Ever prepares to follow, they hear their younger sister Elle's voice calling from inside, begging not to be left alone. Ever lets go of the door and turns back.
The door seals shut, trapping Ever inside. The voice is a recording spliced from a phone call with Elle the previous day, playing from a rigged music box. A note inside repeats the word "WORTHLESS" (185). The realization that someone was near their home and their sister sends Ever into a fury, and they smash the music box.
Outside, Finn pounds his crutch against the reinforced window. Through the glass, he tells Ever he wants to take them on a date when they get out. Ever hesitates, afraid of starting something when Finn is leaving for college, but Finn insists even brief happiness is worth it. Meanwhile, Maddy flees into the surrounding grove, overwhelmed by grief. At the cliff's edge, she discovers both coat pockets filled with pills identical to her painkillers, alongside a note reading "ADDICT" (191). Maddy reflects on how her addiction developed after her accident, escalating from managing physical pain to numbing emotional anguish. The pills are clearly intended to kill her. She speaks aloud to Carter's memory, recalling his belief that scary things are easier when faced with friends, then unclenches her fist and lets the pills scatter onto the moss.
Maddy returns and joins Finn at the window. Together they pound the glass until it shatters. Ever climbs through, and the three embrace. They begin descending the mountain, agreeing the attacker must know their lives intimately. Finn realizes the boulder blockade is the likely site of his intended death, designed to look like an accident. Rather than flee, the three decide to fight back: Finn will act as bait on the boulders, Maddy will ambush with her cloak, and Ever will use Finn's leather belt to help restrain the attacker.
The attacker is Liva. In a chapter narrated from her perspective, she reveals her father raised her to view the world as a hierarchy of predators and prey, teaching her that emotions are weaknesses and attachments must be severed. He made her kill a pet rabbit as a child to prove the lesson. She perceived each friend as a threat: Carter stole money from her father's company, Maddy was deteriorating, Finn demanded more loyalty than she felt she owed, and Ever received opportunities she considered undeserved. She describes the night's violence as a rite of passage, her family's tradition of sacrifice.
At the boulders, the confrontation turns chaotic. Maddy leaps from the trees and throws her cloak over Liva's face. Finn strikes Liva's knee with his crutch. Liva slashes Maddy's arm with a knife and stabs Ever's hand with a second hidden blade. When Liva flings Maddy toward the cliff edge, Finn cuts the belt binding them with a bread knife, freeing Maddy. The sudden release sends Liva stumbling backward over the cliff. Finn reaches for her but is too far away.
The three survivors tend to their wounds and begin walking down the mountain at dawn, sharing the secrets they have been carrying. Maddy confesses her addiction; Finn offers to connect her with his therapist and accompany her to her first appointment. Ever confesses they are dropping out of high school, having failed half their classes while working to support their family. Finn urges Ever to pursue an internship offered by Damien, an older trans game developer and mutual friend. They discuss whether the game is to blame for what happened; Maddy and Finn argue that Gonfalon saved them, that their characters kept them going when real life felt impossible. By a stream near the mountain's base, Finn tells Ever he loves them, though he will wait to kiss them properly. Ever, who has been afraid to pursue happiness, resolves to try. Battered and grieving but together, the three walk arm in arm toward civilization as the sun rises.