''Foucault's Pendulum'' is a 1988 novel by Creator/UmbertoEco, and a notable work of [[AncientConspiracy conspiracy literature]].

While ''TheDaVinciCode'' plays the conspiracy theory view of history completely straight, and ''{{Illuminatus}}'' subverts it wildly, this novel is an [[ViewersAreGeniuses elaborate]] and [[TakeThat sometimes savage]] {{Deconstruction}}.

[[AC: The main characters are:]]
* Casaubon: Protagonist and narrator. Also an intellectual dilettante and expert on TheKnightsTemplar.
* Jacopo Belbo: Editor who is haunted by failure and frustrated desires.
* Diotallevi: Belbo's partner who is obsessed with all things Jewish and Kabbalistic.

The narrative contains numerous flashbacks, dream sequences, and historical anecdotes, but the basic plot is this:

Casaubon, while working on his degree, meets Belbo at a bar one night and they have a conversation during which Casaubon reveals his field of expertise - the history of the ''Poor Fellow-Soldiers of Christ and of the Temple of Solomon'', also known as the Knights Templar. Belbo, who works for a publisher named Garamond who specializes in academic works and doubles as a [[VanityPublishing vanity press]] for various crackpots and assorted nuts with pretensions to intellectualism, finds Casaubon interesting and invites him to visit the publisher. Casaubon is introduced to Diotallevi and is allowed to be present and re-presented as a "topical expert" while they interview an aspiring author, Colonel Ardenti, who presents a manuscript. This turns out to be a book purporting to expose the secret of the Templars, which Ardenti believes to be dangerous knowledge.

Sure enough, the man disappears mysteriously, but the police investigation goes nowhere. Casaubon moves to Brazil, where he hooks up with a radical socialist girlfriend named Amparo and later meets a man named Aglič who is an expert in occultism. Aglič likes to tell historical stories as though he were there in person. Eventually, Amparo leaves Casaubon, and Casaubon moves back to Italy.

Upon his return, Casaubon becomes a freelance researcher and accepts work from Garamond, first on a history of metals, and then a history of occultism. He also meets and falls in love with a woman named Lia. During their projects, he, Belbo, and Diotallevi meet many odd characters from the occult world of conspiracy theories and secret histories, partly with the help of Aglič who has contacts there. Bemused and bored by the inanity of the various conspiracy theories they are require to listen to, read about, and publish, the trio decide one night to fabricate their own arcane history based on the idea that one root occult conspiracy is the cause of all world historical events. This byzantine, chimerical super conspiracy they enigmatically designate "The Plan".

Over Lia's objections, Casaubon and his partners become more and more invested in the Plan they have created, but then unwisely start hinting to Aglič that they possess knowledge he does not. Aglič, Ardenti, and other members of the European occult community decide that they are meant to be in control of history, and start chasing after the (completely synthetic) secret of the Plan, starting by pursuing the trio of protagonists themselves.
!!Provides Examples Of:

* AncientConspiracy / ConspiracyKitchenSink: Played with to SerialEscalation levels.
* AmbiguouslyJewish: Diotallevi
* ArcNumber: 120.
* ArsonMurderAndJayWalking: A really peculiar inversion with the garrulous publisher's habit of starting out hyperbolic in his praise of things and then (apparently without realizing it) taking an abrupt downturn. E.g. "It is a palace! A dwelling fit for kings! I'll put it even more strongly: It's a genuine Piemontese villa!"
** An example done straight is in when Casaubon mentioned the Borborites, who rip out fetuses from women's bodies, crush them in mortars and eat them with honey and pepper. Diotellavi says: "How revolting, honey and pepper!"
* AuthorAvatar:
** A lot of Belbo's stories about his wartime childhood are directly taken from Eco's biography. Especially the trumpet episode.
** Like Diotallevi, Umberto Eco's grandfather was a foundling, and if the book is anything to go by Eco definitely seems to have an interest in Kabbalah.
* BigBad: [[spoiler: Aglič]].
* BilingualBonus
* BolivianArmyEnding: [[spoiler: Diotallevi dies of cancer, Belbo and Lorenza are killed by the Tres members (probably, if Casaubon didn't hallucinate this), and Causabon himself expects that Tres would soon come after him (this is, most likely, a delusion of him, even if everything before this was true)]]
* ConspiracyTheorist: Subverted. The three protagonists all start out as GenreSavvy {{Deadpan Snarker}}s lampooning ConspiracyKitchenSink theories in general, but as the the book nears its end, they become raving {{Conspiracy Theorist}}s themselves, seeing [[WhatDoYouMeanItsNotSymbolic symbolism]] and [[AncientConspiracy dark secrets]] behind absolutely everything.
* DeconstructiveParody: The whole book does this to the ConspiracyLiterature genre. [[LampshadeHanging Lampshaded]] numerous times.
* {{Doorstopper}}
* {{Epigraph}}: Opens each chapter. Most of them are of obscure texts related to the chapter's theme, but there's one about the physics of a hanged man (which is also related to the particular chapter).
** The epigraphs are, of course, the list of 120 quotes repeatedly referenced by Belbo and Casaubon.
* FakeRealTurn: The Plan.
* [[NaziGold Fascist Gold]]: The policeman mentions a ConMan who claimed he had found UsefulNotes/BenitoMussolini's famous treasure in a lake. All he'd need was a bit of starting money...
* UsefulNotes/FascistItaly: Belbo tells long stories from his childhood, which took place during Mussolini's rule.
* FemmeFatale: Lorenza, with a few twists.
* FrenchJerk: Pierre, the French satanist
* GenreDeconstruction: The novel deconstructs all the stories of Conspiracy Theories.
* GoneHorriblyWrong: Belbo, Casaubon and Diotallevi create "The Plan", an elaborate and ridiculously TropeOverdosed ConspiracyTheory as nothing more than a fun project for killing some free time and [[StealthParody for mocking]] all the ConspiracyKitchenSink theories and secret histories they were forced to read while editing the manuscripts of various wacko authors for publishing. Their whole prank gradually starts getting out of hand and [[YourMindMakesItReal sounding]] [[ParanoiaFuel far too real]], since it's often even [[ShownTheirWork more convincing]] than all the [[WhoWritesThisCrap pulp conspiracy theories]] it was supposed to make fun of in the first place. [[spoiler:Then a secret society of whackjobs show up, and they might have [[TheCuckoolanderWasRight been telling the truth by accident all along.]]]]
* HollowEarth: One of the final pieces of the Plan.
* HowWeGotHere: Casaubon's narration.
* {{Kabbalah}}: The branches/spheres of the kabbalistic tree of life serve as chapter headings.
* LastNameBasis: The three main characters.
* LeyLine: Part of the conspiracy theory.
* Loving Force: Subverted. When Amparo, as she told, noticed a guy approaching her in the night on the street, and suspected he wanted to rape her, she offered him to have sex. He ran away, because he wanted to hurt women, not sex.
* NamesGivenToComputers: Abulafia, after the founder of the school of Prophetic Kabbalah.
* NoNameGiven: The first names of Casaubon and Diotallevi are never revealed.
** Casaubon's first name ''may'' be Pim. However, only Lia calls him that, so it might be just a nickname.
* NumerologicalMotif: Lia gives Casaubon a talk about the real meanings. The number one is special because every human is, well, one human and has one head, heart, nose, mouth, private part etc.; two is special because two people make a couple, and humans generally have two hands, feet, eyes, ears etc.; three OTOH is so special because our bodies don't have three of anything (but man + woman + child make a family); etc.
* [[spoiler: OhWaitThisIsMyGroceryList]]: [[DoubleSubversion Double subverted]], thanks to the FakeRealTurn.
* OlderThanTheyLook: Aglič. Maybe.
* [[ViewersAreGeniuses Readers Are Geniuses]]
* RealityIsUnrealistic: The narrator notes how many contradictions and other unexplainable things happen in the story of the Knights Templar, which helped creating the mystery around them:
** ThePope Clemens V prolonged the trial; as the king suspects, to give the knights time to flee. But they don't.
** The king sends his mooks to check the riches of the knights, to make sure he won't lose anything. The knights don't suspect anything.
** Then, the king orders to arrest the knights. It takes one month from order to arrest, but the knights don't flee.
** Almost all the tortured knights confess. Even if you think that they have suffered worse in the war.
** But they only confess if it's demanded by them, and only confess what the inquisitors want to hear.
** Some try to play the accusations down, others confess even worse things than demanded.
** Then, the pope tries to get the control of the trial himself. Does he want to save the knights?
** Later, the king even gives in - but soon after, the pope gives the control back!
* ReallySevenHundredYearsOld: Aglič. Or is he?
* RedemptionEqualsDeath
* TheReveal: When we find out that the mysterious document that the Plan is based on [[spoiler:is basically a grocery list from the late eighteenth or early nineteenth century.]]
* ShakespeareInFiction: Or in {{metafiction}}, at least - Belbo's writings about The Plan include an excessively convoluted theory about Shakespearean authorship.
** Written in a narrative style with Belbo imagining himself as a reincarnation of the true original writer.
* ShoutOut: Hundreds if not thousands of them. Belbo's files are especially crammed: one reads like a crazy {{Troperiffic}} pastiche in which each paragraph (maybe each line) references a different nineteenth century adventure, mystery or conspiracy story. Did we say GeniusBonus?
* StylisticSuck: Belbo's own attempts at litterature are quite awful. He is very aware of this and doesn't want anyone to read them. His only "good" pages are when he abandons the Plan for his chilhood memories.
* TakeThat: A strong one against conspiracy theories and those who believe in them.
* TaxidermyIsCreepy: The narrator meets the taxidermist Salon in his shop and feels very creeped out.
* ThePasswordIsAlwaysSwordfish: Played with. Casaubon tries to figure out the password to Belbo's computer, which asks: "Do you know the password?" Since Belbo is his close friend, he tries numerous expressions he thinks Belbo could've used, but none of them work. Eventually, he angrily types: "No." This is the password. (There's a deeper reason for this: In order to gain knowledge, you have to admit that you don't know a specific thing.)
* ThereAreTwoKindsOfPeopleInTheWorld: When Casaubon and Belbo meet for the first time, Belbo talks about how there are four kinds of people in the world: "cretins, fools, morons, and lunatics."
* ThroughTheEyesOfMadness: Casaubon, by the end, doubts his own sanity, and questions how much is true of what he had seen.
* VanityPublishing: In-story, there is the publishing house of Garamond doing this. The owner also changes the business model: he makes the occultists and conspiracy nutters pay to have their books published, '''and then sells the books'''.
* WomenAreWiser: Lia. She rejects all conspiracy theories, explains that there are very simple reasons for {{Numerological Motif}}s and the document the whole Plan was based upon is [[spoiler:simply a very old laundry list]].