In a dark and intriguing narrative, seasoned rare book dealer Dean Corso, portrayed by Johnny Depp, finds himself ensnared in a mysterious web of deception and ancient secrets. Hired by the enigmatic Boris Balkan, a wealthy collector driven by an insatiable thirst for the unknown, Corso's task is to validate the authenticity of one of three existing copies of The Nine Gates of the Kingdom of Shadows. This notorious tome was crafted in collaboration with the Devil himself by 17th-century author Aristide Torchia. Its dark reputation is only rivaled by its rarity, with Balkan believing that only one of the three copies is truly genuine.
As Corso embarks on this perilous journey to uncover the truth, he becomes entangled with a captivating and enigmatic figure known simply as The Girl, whose motivations remain shrouded in mystery. His travels lead him to Liana Telfer, played by Frank Langella, the alluring widow of Andrew Telfer, who previously sold The Nine Gates to Balkan before taking his own life. Corso's encounter with Telfer is nothing short of a masterclass in seduction where she tries to convince him to part with the book, only to be rebuffed and later violently confront him.
The following morning, Corso stumbles upon a deeply unsettling discovery at the bookstore where he entrusted The Nine Gates: the bookseller has been hanged in a grotesque reenactment of one of the engravings from the very book itself. Disturbed yet undaunted, Corso retrieves the rare tome and journeys to Toledo, Spain, to meet the Ceniza Brothers, renowned book restorers with links to Balkan's copy. They reveal a shocking revelation: only six of the book's nine engravings are signed "A.T." for Aristide Torchia, while the remaining three bear the ominous initials "L.C.F.," echoing with foreboding significance.
As Corso dives further into the mystery, he comes to realize that The Nine Gates may hold more than mere ancient knowledge; it could be a gateway to eternal damnation. His quest takes him to Sintra, Lisbon, where he encounters Victor Fargas, the enigmatic owner of a copy of the book. Upon examining his own copy, Corso discovers that three peculiar engravings are signed "L.C.F.", differentiated by subtle details from those attributed to "A.T.". When he shares this finding with Balkan, he is sent to obtain Fargas' rare version. Soon after, The Girl accompanies Corso on a solemn visit to Fargas' grave, only to discover his charred remains alongside the very burned copy of The Nine Gates, now missing the three "L.C.F." engravings.
Corso's investigation leads him to Paris, where he seeks the Baroness Kessler, the keeper of another prized copy. Her cautious demeanor stems from her awareness of Corso's connection to Balkan, resulting in her refusal to grant him access. After narrowly escaping a vicious attack outside, he is saved by The Girl, whose exceptional abilities seem almost supernatural. In an attempt to hide Balkan's copy from prying eyes, Corso conceals it in his hotel room and shares his theories about the "L.C.F." engravings with Kessler, conjecturing that each copy has engravings that, when combined, reveal a cohesive set of nine. Intrigued, Kessler permits him to inspect her copy, but tragedy strikes when Corso is ambushed, and the Baroness meets a fatal end at the hands of an unseen attacker, who sets her lavish library ablaze. Returning to his hotel room, Corso is horrified to find that Balkan's precious book has vanished, presumably stolen by Liana.
In their relentless pursuit of Liana, Corso and The Girl arrive at a foreboding manor where a secretive cult is enacting a dark ritual using Balkan's ominous tome. Sensing the disturbance, Balkan interrupts the ceremony to reclaim his sacred book, silencing Liana in a deadly manner as the cult members flee in fright. Mistakenly believing that The Girl had betrayed him, Corso abandons her and chases after the cunning cult leader, only to lose him when his vehicle breaks down on a lonely road.
Undeterred, Corso uncovers a cryptic clue among Kessler's possessions that leads him to a remote and eerie castle. There, he finds Balkan preparing to summon the very depths of hell through the ancient "L.C.F." engravings. The cult leader subdues Corso, forcing him to watch the ritual unfold; seemingly, it grants Balkan unfathomable powers and imperviousness to harm, compelling him to self-immolate in a desperate attempt to prove his newfound strength to the doubtful Corso.
Yet, the ritual's outcome proves uncertain as Balkan writhes in agony within the flames. Ultimately, Corso manages to escape, reclaiming the engravings and ending Balkan's torment with a bullet. Amidst the ruins of Balkan's vehicle, The Girl reappears, claiming him with a passionate kiss that foreshadows their descent into lunacy.
As they journey through the night, The Girl confides in Corso about the truth behind Balkan's failed ritual: one engraving was a forgery, rendering the entire endeavor futile. When she mysteriously vanishes at a gas station, leaving behind only a cryptic note, Corso is left to decipher the growing enigma. His exploration leads him back to the Ceniza brothers' shop, only to discover they have inexplicably vanished, alongside any trace of them.
As workers clear out the deserted store, a dusty paper drifts down, revealing an authentic engraving that depicts a woman resembling The Girl riding a dragon-like beast, set against the very castle that hosted Balkan's doomed incantation. Corso returns to the castle at dawn, and as the gates open to a blinding light, it is evident that the Ninth Gate has finally swung open for him, beckoning him towards a path of enlightenment and darkness.
