Hannah, a medical intern in West Los Angeles, is tormented by layered nightmares about her boyfriend Ben's death. A year earlier, Ben, a wildlife photographer, was killed during a winter backpacking trip in Northern California. Hannah tried to drag his body through the snow but gave up and saved herself. A truck driver found her near death on a road, and a search party never recovered Ben's remains. Since then, she has been medicating with Xanax, isolating from friends, and experiencing waking hallucinations she describes as "Russian nesting dolls filled with memories" (7).
Her crisis deepens when exhaustion and Xanax cause her to set a patient's morphine drip incorrectly, triggering a code blue. Her attending physician places her on indefinite leave. Her psychiatrist, Dr. Grady, urges residential treatment, but Hannah resists. Her best friend, Tess, arrives uninvited with a birthday invitation to Avidya Healing Retreat, an exclusive, tech-free compound near Joshua Tree led by a figure called Guru Pax. After consulting Grady, Hannah agrees to go.
The group includes Tess, a spiritual-creative influencer; Luna (born Lauren), a yoga teacher; Jared, Luna's advertising-executive boyfriend; and Miles, a touring DJ with whom Hannah shares unresolved romantic tension. During a stop in Joshua Tree, an old man at a mining museum tells Hannah the basic legend of Waylon Barlow, a ruthless bank robber who disappeared into the desert in the 1890s, and recites a grim children's rhyme: "He'll hack you up without a trace, pick your bones and steal your face" (53). At a dive bar, Jared antagonizes Lance Corporal Dennings, a hostile Marine who resents outsiders.
Pax, a white man in a white linen jumpsuit, welcomes the group to the torch-lit retreat. His assistant, Kimi, a young Indigenous woman, collects their phones and car keys. On the first night, each participant walks a stone labyrinth to declare a one-word intention. Hannah chooses "Release." Pax tells her with unnerving precision that she is "frozen" and must grieve to find freedom. Dennings follows the group's car to the retreat that night to vandalize it, part of a vigilante pattern the local papers call the J-Tree Terror. An unseen attacker kills him with a pickaxe and carves off his face.
The next morning, Pax leads a sound bath, a meditative session with singing bowls, while Kimi burns bundles of dried leaves. Pax whispers personalized prompts that trigger vivid re-experiences of each participant's deepest trauma. Hannah relives the mountaintop where Ben proposed. During a yoga class, Jared grows jealous of Pax's physical attention to Luna and throws a punch. In a chapter from Jared's perspective, he retreats to the sweat lodge and begins reflecting on his desire to change. Someone seals him inside, forces a rattlesnake through the vent into his mouth, and drowns him in the scalding hot springs after he crawls out. The group discovers only that Jared and the Range Rover are gone; Luna assumes he left in typical spite.
Pax announces an overnight wilderness hike. Kimi prepares an "elixir" described as psychoactive, and participants sign waivers. Alone in a boulder field, Hannah discovers the entrance to Dead Man's Due Mine. A figure in a wide-brimmed hat, suspenders, and a mask of human skin emerges dragging a pickaxe and slashes her forearm. She flees and collides with Miles. Back at camp, Kimi recounts the full Barlow legend: A cave-in trapped the entire gang inside the mine, and Barlow survived for weeks by cannibalizing his companions, wearing his last victim's face when rescuers found him.
In a chapter from Luna's perspective, she practices yoga alone. Barlow enters silently and snaps her spine backward over a pickaxe pressed to her back. Her disappearance is covered by a forged note. During a visit to Kimi's yurt, Hannah discovers that Kimi's reserved persona is a performance Pax demands and that her real name is Kimberly. Kimi reveals the spirit journey elixir was just chamomile tea, meaning Hannah's desert attack occurred without hallucinogenic influence. She warns that the retreat "is not what you think it is" (179) and returns Hannah's phone. Hannah discovers that the "sage" Kimi burned during the sound bath was actually salvia divinorum, a psychoactive plant that induces intense hallucinations when inhaled. Pax drugged the group during the sound bath while using the placebo elixir as misdirection.
Hannah hikes to a mountaintop for cell service and reaches Grady, who confirms the salvia, but her phone dies. Miles joins her investigation, and they sneak into Pax's yurt, finding manipulation manuals and a hidden key fob. Hiding under the bed, Hannah overhears Pax on a satellite phone discussing "candidates" ready to "transcend." That night, they find the Range Rover hidden in the desert with both Jared's and Luna's bags inside. Hannah confides what she has never told anyone: She refused Ben's proposal, and when he stormed off and recklessly approached a herd of elk, the bull gored him through the chest. Hannah froze and watched him die, then placed the ring on her own finger. Miles responds with compassion, and they kiss. When Miles begins acting erratically, Hannah realizes he is high on ecstasy and drives back alone. Left behind, Miles discovers someone spiked his water with his own pills. He finds Dennings's faceless corpse, then stumbles back to the retreat, where Barlow kills him by dropping a bronze gong disk through his neck.
Hannah and Tess find a hidden surveillance camera. Using the key fob, Hannah opens a concealed door behind the retreat's water feature, revealing a control room with live camera feeds and dossiers compiled from stolen personal data. Pax confesses his real name is Paul, a fired software engineer who built Avidya to demonstrate data-mining technology as a corporate wellness product for tech investors. Hannah knocks him unconscious. Barlow subsequently kills Paul, impaling him with a pickaxe, electrocuting him with his own stun baton, and driving his face onto an amethyst crystal.
Hannah discovers each friend's corpse staged in a grotesque tableau throughout the retreat. In the labyrinth, she swings a dagger at what she believes is Barlow but stabs Tess in the stomach. Seeing Barlow's reflection overlaid on her own in a mirror, she briefly believes she is the killer. She flees in the Range Rover but crashes after swerving to avoid Barlow in the road.
Trapped in the wreck, Hannah hallucinates Ben one final time. He tells her to leave him and live, or stay and die. She refuses to die. Dr. Grady pulls her from the burning vehicle, claiming he came after her distress call, but Tess arrives wounded and identifies Grady as the killer. Grady confesses: He became obsessed with Hannah during their sessions, killed her friends to isolate her, engineered new trauma to forge a permanent bond, and planned to have her committed under his permanent control. He forced Kimi into the Barlow costume at gunpoint and spiked Miles's water with Miles's own pills. Grady shoots Tess, but she survives. Kimi, still conscious, plays loud music to distract him. Hannah splashes Tess's highly flammable essential oils into Grady's eyes, and Kimi disarms him. Hannah ignites his oil-soaked face with a torch. The three survivors drive out of the desert in the dead Marine's vehicle.
In the epilogue, Hannah visits Ben's grave for the first time since his funeral. She visualizes carrying his body out of the wilderness and burying him. She removes the engagement ring and places it on the headstone. "I'm done carrying you," she says (282). She walks away having achieved her mantra not through gurus or spirits, but through her own agency.