Scott McGrath, a once-celebrated investigative journalist, is jogging around the Central Park Reservoir after two in the morning on a rainy October night when he notices a woman in a vivid red coat flickering in and out of the lamplight. Her face hidden by dark hair, she appears on the North Gatehouse landing, staring down at him. After he boards a subway, he sees her descending the station stairs just as the doors close.
Days later, McGrath receives a text informing him that Ashley Cordova, the 24-year-old daughter of reclusive cult filmmaker Stanislas Cordova, has been found dead in a Chinatown warehouse, an apparent suicide. Five years earlier, McGrath accused Cordova on national television of being a predator, citing an anonymous caller named "John" who described the director visiting elementary schools at night to collect children's belongings. The call could not be verified. Cordova's attorneys sued for slander, costing McGrath his career, his reputation, and $250,000. McGrath resolves to investigate Ashley's death as a path to exposing her father.
McGrath obtains Ashley's NYPD case file from Detective Sharon Falcone, a longtime contact. The file reveals Ashley was admitted to Briarwood Hall, a private psychiatric hospital, in late August, classified at the most acute level of care. On September 30, she escaped with an unidentified man, ten days before her death. McGrath also consults Wolfgang Beckman, a Columbia film professor and devoted Cordovite. From Beckman's computer, McGrath secretly photographs the URL of the Blackboards, a hidden deep-web fan site where anonymous devotees share testimonies about Cordova.
Two allies join the investigation. Nora Halliday, a 19-year-old coat-check girl at the Four Seasons, was the last person to see Ashley alive. She reveals she kept Ashley's distinctive red-and-black coat, which McGrath recognizes as the one worn by the woman at the Reservoir, realizing Ashley had been following him before her death. Hopper Cole, a 25-year-old drifter, turns up at the warehouse; Ashley mailed him a stuffed monkey just before she died. Hopper knew her from a wilderness therapy camp in Utah, where she was fearless and fiercely protective of weaker campers. McGrath reluctantly accepts both as partners.
The trio traces Ashley's movements. At Briarwood, a nurse throws herself in front of their car, shouting the name Morgan Devold. Devold, a former security guard, helped Ashley escape after watching her play piano nightly on security cameras. At the Waldorf Towers, a housekeeper describes finding Ashley unconscious and seeing a second pupil-like mark in her left eye she calls "evil's footprint." At Klavierhaus, a piano showroom, the manager recounts two visits: Ashley played brilliantly the first time but returned unkempt and despairing. She signed the guest book as "Kay Glass," a character from one of Cordova's films, listing an address at 83 Henry Street. In that Lower East Side tenement, the trio finds Ashley's room containing concentric circles of black ashes and knotted roots above the door. At Enchantments, a witchcraft store, an expert named Cleopatra identifies these as evidence of an uncrossing ritual. Cleopatra also discovers a killing curse on the soles of their shoes.
They spot Cordova's son Theo, recognizable by a left hand missing three fingers, following them through lower Manhattan. A cryptic poem on the Blackboards leads them to Oubliette, a secret bondage club in a Montauk mansion, where McGrath learns Ashley broke in and attacked a member known as "the Spider."
Hopper's true connection to Ashley emerges when Nora notices a matching half of a split tattoo on his ankle depicting a kirin, a mythical guardian creature. Hopper confesses he and Ashley were in love. They corresponded for years after camp and planned to run away to Brazil, but her family discovered the plan and took her away. She sent an email ending things, and Hopper believed it until she mailed him the stuffed monkey, which had belonged to a boy named Orlando who drowned at the camp partly because of Hopper's cruelty.
Cross-referencing the Waldorf guest list with the Oubliette membership, they identify the Spider as Hugo Villarde, who owns an antiques shop in Spanish Harlem. Villarde, an imposing man in priest's clothing with burn scars on his face, confesses that Ashley tracked him down and confronted him. During the visit, McGrath's five-year-old daughter Sam is injured by a falling lamp, and McGrath's ex-wife, Cynthia, moves to restrict his visitation rights.
Marlowe Hughes, Cordova's reclusive second ex-wife, reveals the history of The Peak, Cordova's isolated Adirondack estate built on a massacre site. Cordova became involved in occult rituals practiced by local townspeople, and his first wife drowned herself upon learning the truth. Marlowe explains that at age five, Ashley was led across a "devil's bridge" by Villarde out of jealousy. Afterward, her piano playing became superhuman, her body ran perpetually cold, and a dark mark appeared in her eye. Cordova spent years trying to save her, visiting schools at night to collect children's belongings for a soul exchange, exactly as "John" had described. At Enchantments, Cleopatra determines that a black figurine found in Sam's coat pocket contains a protection spell. Ashley had given talismans to three children during her final days, shielding them from her father's exchange attempts.
The trio breaks into The Peak by canoe. McGrath is chased by dogs into vast soundstages containing intact film sets. Inside a greenhouse set, he unknowingly contacts highly toxic hallucinogenic plants. He enters underground tunnels, crosses the devil's bridge, and sees a trench filled with decomposed children's belongings. Robed figures capture him. He wakes inside a hexagonal wooden box, escapes by breaking through nested compartments, and is found on a roadside three days later.
The evidence collapses. Lab tests reveal the stained shirt McGrath found contains corn syrup, not blood, and recovered bones belong to a bear cub. The toxic plants call into question everything he witnessed. Every witness vanishes: Devold's house has burned down, employees have quit, phones are disconnected, and former contacts have cut all communication.
McGrath confronts Inez Gallo, Cordova's devoted assistant, at the family townhouse. Gallo reveals Ashley had acute lymphoblastic leukemia, a cancer she battled since age five. The family kept it secret at Ashley's insistence. Her musical genius, her disappearances, and her erratic behavior all stemmed from her disease and its treatments, not a devil's curse. Gallo claims Cordova became catatonic after learning Ashley was terminally ill again and now resides in a nursing home under an alias. McGrath visits the facility, finds a large, silver-haired man in a wheelchair, sits beside him in silence, and leaves.
Yet McGrath cannot fully accept this explanation. He reunites with Hopper and Nora for Nora's theatrical debut, choosing not to share the cancer diagnosis. Cynthia agrees to let Sam visit, and Sam confirms Ashley left the protective figurine in a playground. McGrath suspects the man in the nursing home was a decoy, recalling Beckman's warning about a Cordova trademark: a substitute positioned at the intersection of life and death to grant freedom to the real thing. Following embedded clues, McGrath travels to Chile. On a remote island, he finds a small house containing a burning Murad cigarette, Cordova's signature black-lensed glasses, and a bottle of McGrath's own scotch. A hulking figure appears in the doorway. McGrath steps toward him, ready to listen.