The main characters are:
- Casaubon: Protagonist and narrator. Also an intellectual dilettante and expert on The Knights Templar.
- 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 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 Agliè who is an expert in occultism. Agliè 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 Agliè 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 Agliè that they possess knowledge he does not. Agliè, 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:
- Affectionate Nickname: Lia calls Casaubon "Pow".
- Ancient Conspiracy / Conspiracy Kitchen Sink: Parodied and deconstructed. The protagonists make up a parody conspiracy theory to make fun of real ones; however, they soon start to believe in it themselves, and besides, they become targets for a very real group of occultists and conspiracy theorists who buy into their hoax and start chasing after them.
- Ambiguously Jewish: Diotallevi. His grandfather was a foundling, discovered near a Jewish ghetto, he loves Kabbalah, and really wants to believe he's Jewish; it remains ambiguous though whether he really is.
- Arson Murder And Jay Walking:
- Inverted 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!"
- Casaubon mentions 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!"
- Author Avatar:
- 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.
- Big Bad: Agliè, who is revealed to be the leader of a sinister neo-Templar group.
- Contemptible Cover: A verbal variant. The protagonists use a computer nicknamed Abulafia to create the Plan. Some editions have blurbs calling Abulafia an immense computer, but really it's just a desktop model.
- Conspiracy Theorist: Subverted. The three protagonists all start out as Deadpan Snarkers lampooning Conspiracy Kitchen Sink theories in general, but as the the book nears its end, they become raving Conspiracy Theorists themselves, seeing symbolism and dark secrets behind absolutely everything.
- 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).
- Gone Horribly Wrong: Belbo, Casaubon and Diotallevi create "The Plan", an elaborate and ridiculously Trope Overdosed Conspiracy Theory as nothing more than a fun project for killing some free time and for mocking all the Conspiracy Kitchen Sink 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 sounding far too real, since it's often even more convincing than all the pulp conspiracy theories it was supposed to make fun of in the first place. Then a secret society of whackjobs show up, and they might have been telling the truth by accident all along.
- Kabbalah: The branches/spheres of the kabbalistic tree of life serve as chapter headings.
- Kill Em All: Diotallevi dies of cancer, Belbo and Lorenza are killed by the Tres members (probably, if Casaubon didn't hallucinate this), and Casaubon himself expects that Tres would soon come after him (this is, most likely, a delusion of him, even if everything before this was true).
- Last-Name Basis: The three main characters.
- Ley Line: Part of the conspiracy theory. The Plan assumes that The Knights Templar learned to harness the power of the ley lines.
- Local Hangout: Casaubon, Belbo and Diotavelli go to Pilade's Bar sometimes to discuss about their research.
- Mockspiracy: The protagonists invent a centuries-old conspiracy involving Rosicrucians, Templars, Masons and other secret organizations to parody the real-life conspiracy theorists. Zig-Zagged however, since the real occultists and conspiracy theorists take the story at face value, and actually create the secret society that the protagonists made up.
- Names Given to Computers: Abulafia, after the founder of the school of Prophetic Kabbalah.
- Nazi Gold: The policeman mentions a Con Man who claimed he had found Benito Mussolini's famous treasure in a lake. All he'd need was a bit of starting money...
- Never Found the Body: Ardenti. It turns out that he's alive and he's one of the Diabolicals.
- No Name Given: The first names of Casaubon and Diotallevi are never revealed.
- Numerological Motif: 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.
- The Password Is Always "Swordfish": 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.
- Pop Culture Symbology: The book, which is a savage deconstruction of conspiracy fiction, has the protagonists inventing a parody conspiracy theory that connects Templars, Rosicrucians, Freemasons, etc., as well as modern-day fiction and cartoons.
- Reality Is Unrealistic: Casaubon notes how many contradictions and other inexplicable things happen in the story of the Knights Templar, which helped creating the mystery around them:
- The Pope 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 the knights arrest. It takes one month from order to arrest, but the knights don't flee.
- Almost all the tortured knights confess. Even though they've suffered worse in the war.
- But they only confess if it's demanded of 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!
- The Reveal: When we find out that the mysterious document that the Plan is based on is basically a grocery list from the late eighteenth or early nineteenth century.
- Sage Love Interest: Lia is presented as the epitome of "natural wisdom", in contrast to the pseudo-profound concepts of the Diabolicals.
- Secret History: In-Universe, with the editors constructing a fake conspiracy.
- Shakespeare in Fiction: Or in metafiction, at least - Belbo's writings about The Plan include an excessively convoluted theory about Shakespearean authorship.
- Shout-Out: 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 Genius Bonus?
- Stylistic Suck: Belbo's own attempts at literature 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 childhood memories.
- Take That!: A strong one against conspiracy theories and those who believe in them.
- Taxidermy Is Creepy: The narrator meets the taxidermist Salon in his shop and feels very creeped out.
- The Teetotaler: Diotavelli refuses to drink alchol in Pilade's.
- There Are Two Kinds of People in the World: 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.""There are four kinds of people in this world: cretins, fools, morons, and lunatics Cretins dont even talk; they sort of slobber and stumble Fools are in great demand, especially on social occasions. They embarrass everyone but provide material for conversation Fools dont claim that cats bark, but they talk about cats when everyone else is talking about dogs. They offend all the rules of conversation, and when they really offend, theyre magnificent Morons never do the wrong thing. They get their reasoning wrong. Like the fellow who says that all dogs are pets and all dogs bark, and cats are pets, too, therefore cats bark Morons will occasionally say something thats right, but they say it for the wrong reason A lunatic is easily recognized. He is a moron who doesnt know the ropes. The moron proves his thesis; he has logic, however twisted it may be. The lunatic on the other hand, doesnt concern himself at all with logic; he works by short circuits. For him, everything proves everything else. The lunatic is all idée fixe, and whatever he comes across confirms his lunacy. You can tell him by the liberties he takes with common sense, by his flashes of inspiration, and by the fact that sooner or later he brings up the Templars There are lunatics who dont bring up the Templars, but those who do are the most insidious. At first they seem normal, then all of a sudden "
- Through the Eyes of Madness: Casaubon, by the end, doubts his own sanity, and questions how much is true of what he had seen.
- Vanity Publishing: 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. And when the books don't sell (for obvious reasons), the publisher threatens to destroy the remaining copies, but offers the authors the chance to buy the lot to distribute on their own. In essence, the authors pay for their books twice!
- Viewers Are Geniuses: To give some illustration of the sheer magnitude of the permeation of this trope through his fiction, Foucault's Pendulum requires at least a modest familiarity with the conception of God in Kabbalah in order to understand the book's narrative arrangement; and though Kabbalah is hardly the most obscure of topics—and certainly not the most obscure form of knowledge required to understand Foucault's Pendulum—this novel requires substantial reading into a major world mystic/faith tradition merely to understand its chapter layout.
- Women Are Wiser: Lia rejects all conspiracy theories, explains that there are very simple reasons for Numerological Motifs and that the document the whole Plan was based upon is simply a very old laundry list.
- World of Mysteries: Parodied and deconstructed; by the end of the novel, Casaubon starts seeing our real world as this. Lampshaded in the scene at the museum, where he sees nearly every museum exhibit as having some sort of hidden meaning related to Agartha, Count of St. Germain, or other mystical/conspiracy subjects.