Dean Corso (Johnny Depp) is a rare books-dealer whose motivation is only for financial gain. He swindles a naïve couple from a set of rare and priceless books, narrowly beating out a rival dealer. A very rich book collector by the name of Boris Balkan (Frank Langella) hires Corso to validate his recently purchased copy of The Nine Gates of the Kingdom of Shadows by 17th century author Aristide Torchia. It is one of only three copies that exist in the world. The book contains nine engravings which, when correctly deciphered and the interpretations properly spoken, are supposed to summon the Devil. Balkan claims the book may be a forgery, and hires Corso to travel to Europe, assess the other two known copies, find out whether any are genuine and if so, acquire them for Balkan.
Balkan’s copy originally belonged to Andrew Telfer, who committed suicide shortly after selling the book. Corso repeatedly encounters his wife, Liana Telfer (Lena Olin), who wants the book back and is willing to do anything to get it. Once he has the book in his possession, his apartment is ransacked and Bernie (James Russo), his friend and a book store owner, is murdered in the style of one of the engravings in The Nine Gates.
Corso travels to Spain and talks to the Ceniza brothers (Jose Lopez Rodero) who inform him that some of the book’s engravings are signed “LCF,” which could possibly mean “Lucifer.” Corso visits with Victor Fargas (Jack Taylor) and compares Balkan’s copy with his and notes several variations in the engravings. Corso returns the next day to find Vargas murdered and the engravings ripped out of his copy of The Nine Gates. Corso crosses paths with a mysterious woman (Emmanuelle Seigner) who rescues him from an attack by Telfer’s bodyguard (Tony Amoni).
In Paris, Corso tracks down the third surviving copy owned by Baroness Kessler (Barbara Jefford). He records additional differences in her copy before she is killed and pages from her book are removed. He realizes that the secret to the Nine Gates can be found in a combination of all three copies of the book. Telfer steals Balkan’s copy from Corso and he follows her to a mansion where he witnesses her leading a Satanist ceremony. Balkan interrupts the ceremony suddenly, kills Telfer, takes the engravings and the book and drives off to prepare to open the Nine Gates himself. He fails to do so and is consumed by flames during the invocation. The mysterious girl has sex with Corso and points him in the direction of the final authentic engraving thereby allowing him to travel through the ninth portal at the film’s conclusion.