When that happens, you should cut them off quickly — and then dash right out to the bookstore and buy it. Dan Brown’s novel is an ingenious mixture of paranoid thriller, art history lesson, chase story, religious symbology lecture and anti-clerical screed, and it’s the most fun you can have between the sort of covers that aren’t 300-count Egyptian cotton.

If the idea of a mystery that draws on the history of religion and art sounds like the kind of “must read” you’ve picked up before only to find yourself bored silly (i.e., Umberto Eco’s “The Name of the Rose”), let me hasten to reassure you that Brown, for all the facts he throws around, operates squarely in the territory of the pop bestseller. “The Da Vinci Code” doesn’t offer the kind of solid descriptive writing you find in the work of the best practitioners of crime fiction. Brown appears to be the kind of writer who hits on a snazzy gimmick and then mines it for all it’s worth. And it’s one hell of a gimmick.

Brown’s hero is Robert Langdon, a Harvard professor of religious symbolism who, after a lecture in Paris, is awakened in his hotel room in the middle of the night by a member of the Police Judiciare. After being spirited away to the Louvre, he finds that the museum’s curator, whom he was scheduled to meet with earlier in the evening, is dead of a bullet to the stomach. In the time before his death, the curator has managed to leave a trail of clues, the most visible of which is that he has arranged his body in emulation of Leonardo da Vinci’s “The Vitruvian Man.” He has also drawn a pentacle on his chest in his own blood, and scrawled another cryptic message — “O, Draconian devil! Oh, lame saint!” — beside his body in black-light pen.

No sooner has Langdon begun to unravel the possible meanings of the dead man’s clues than he discovers that the grandstanding police captain (whom Brown has given the great name of Bezu Fache) suspects him of the murder. Langdon’s temporary salvation comes in the form of Sophie Neveu, a police cryptologist summoned to the scene who knows Langdon is being set up as the fall guy. Their only chance of following the trail left for them is to go on the lam.

If all that sounds insanely complicated, consider that I haven’t even mentioned the assassin, an albino giant who is also a devout member of the Catholic secret society Opus Dei. Or that the bishop who heads Opus Dei is summoned to a secret meeting with Vatican officials. Or that, like Leonardo himself (and Botticelli and Isaac Newton and Victor Hugo and Jean Cocteau), the dead curator was a member of another secret society, the Priory of Sion. Or the fact that Sophie Neveu is the dead man’s granddaughter.

The fun of “The Da Vinci Code” is that things get even more complicated than that. As in his previous novel, “Angels & Demons” (which also featured Robert Langdon), Brown has written the story in real time. The book is one continuous chase — by car and plane, from Paris to London and back to Paris — with Langdon and Sophie in one “Beat the Clock” situation after another, putting their prodigious noggins to work on the coded clues they’ve been left while staying out of the clutches of Bezu Fache.

That sense of constant forward motion is how Brown manages to disgorge huge chunks of information about history, aesthetics and religious and pagan symbolism without making the book feel like it has stalled in its tracks. (Finding a way to manage that is going to be the biggest challenge for whoever makes the inevitable movie version.) Without giving the game away, I’ll just say that Brown has devised a series of situations that allow the two characters to show off their specialized areas of knowledge, coded clues that allude to the history of art and the tension between paganism and the Catholic Church.

At its best, “The Da Vinci Code” is the type of thriller that might have amused that great atheist Luis Buñuel. Langdon is forever discoursing on symbols — the pentacle, with its connotations of satanic worship, is the best example — whose real meanings have, he insists, been perverted by the church in an attempt to solidify its power by crushing dissent. Central to Rome’s consolidation of power is a suppression of all forms of goddess worship, and a wholesale recasting of pagan iconography in Christian terms.

Part of the fun of conspiracy theories is that they indulge our worst fantasies of the powerful, allowing us to imagine them as the unscrupulous bastards we always suspected they were. And if conspiracy theories have their safe side, offering us a world where everything falls neatly into place, they also promise a weird sort of freedom. Suddenly there are symbols everywhere just waiting to be deciphered, offering revelation to all who can read them. All that we believed fixed is shattered and everything is up for grabs. What could be scarier or more thrilling than that?

“The Da Vinci Code” plays with the gleefully heretical notion that the entirety of Judeo-Christian culture is founded on a misogynist lie, evincing disgust for sex in general and the female body in particular. Brown has a provocateur’s talent for using facts as the seasoning in his sinister stew. He writes of Opus Dei’s $47 million world headquarters in New York as if he were a Jedi describing the Death Star. There’s a bad-boy charge to Brown’s relation of the story of the Emperor Constantine’s unification of Rome under Christianity.

Jesus’ divinity is not, Brown tells us, a sign of God but rather something decided upon by a vote (“a relatively close vote at that,” says one character at Constantine’s ecumenical gathering, the Council of Nicaea). As for the revealed word of God, well, Brown says, what we know as the Bible was created from Constantine’s suppression of all the gospels that related Jesus’ human traits. If you know someone who was upset by Martin Scorsese’s film “The Last Temptation of Christ,” “The Da Vinci Code” should make them fall down frothing at the mouth.

Brown doesn’t stop there. He is at his most wicked in a long section explicating Leonardo’s “The Last Supper,” one of the revered pieces of Christian iconography, which here stands revealed as a two-fingered salute to church doctrine, a pagan critique of the very foundations of Christianity. Boy, is it fun.

But the problem with conspiracy theories is that, in order to keep existing, they need to hover just beyond the reach of exposure. Finally, “The Da Vinci Code” does not have the courage of its anti-clerical provocations. The church has a lot to answer for here, but it’s not the book’s ultimate villain, and as the story draws to a close you sense Brown backpedaling.

There are other, smaller letdowns. As a character, Langdon doesn’t exist as a great deal more than a fount of information. (Brown’s invention of a People magazine description of his hero as “Harrison Ford in Harris tweed” feels like a bid to get Ford cast in the movie version — please, God, no.) And he falls into the danger that always awaits a thriller writer so adept at twists, by supplying so many last-minute surprises he nearly twists the plot into total implausibility.

Finally, though, neither Brown’s failure of nerve nor the slight defects of craft are enough to ruin the pleasure of this hugely entertaining book. As a thriller writer, Brown is like a showboat academic, using facts to spin one grand theory after another. It may be an inch deep, but it has the thrill of a terrific performance. I hope Langdon returns in another adventure, one in which his creator goes whole-hog with his craziest heretical impulses. For all the readers who are going to be happily immersed in “The Da Vinci Code,” that would be a most fitting act of contrition.

Guardian readers have already ably dismantled the straw men in Docx’s essay. I don’t agree with most of what he says, but he has a point when he suggests that the other side often resorts to arguments as trumped up as his own. In fact, ferocious defenders of genre fiction seem far more numerous to me than its (public) detractors, and Docx may have even done them a favor; they seem to enjoy their indignation an awful lot. The not-so-secret reason why pissing matches are so common, after all, is that some people just really love taking it out.

Instead of getting into all that, however, let’s consider the original source of Docx’s concern: the enormous popularity of Larsson’s Millennium Trilogy and the novels of Dan Brown. Certainly, these writers are far from the best their genres have to offer. Even the most vehement of genre champions will not argue that either man is a good, or even adequate, stylist. (Larsson himself seems to have been well aware that he was no Hemingway.) Rather, they are both, in many respects and apart from the whole genre question, fairly bad writers. So why do so many people devour their books?

I pose this question as someone who enjoyed all three of Larsson’s books, although I don’t care for Brown’s. I am exactly the sort of person who might be glimpsed reading “The Girl With the Dragon Tattoo” on a train. Docx seems to think his fellow citizens only resort to these books because they aren’t aware of the much better ones out there. “We simply have to find a way to bring the finest writers of the language more often to the attention of the carriages of people up and down the country who are evidently still willing and able to buy novels for the journey,” he writes. These hapless souls are currently being “subjected” to “atrociously bad” thrillers when they could be immersed in such Docx favorites as “Franzen, Coetzee, Hollinghurst, Amis, Mantel, Proux, Ishiguro, Roth.”

Now, I’m not only aware of all of those novelists, I’ve read much of their work, too; some of it I love, and some of it I don’t. Yet this didn’t stop me from reading Stieg Larsson with a considerable amount of pleasure. Most people who read a lot also read to satisfy a wide spectrum of moods and hankerings, and sometimes trash (provided it’s sufficiently engaging) is just the ticket. This taste, like any other, can be highly idiosyncratic. My friend Lev can’t abide Larsson, while I have in turn needled him for enthusing over a — to my mind — cheesily hard-boiled action-adventure fantasy novel. (Also: He claims to be a “Twilight” fan.)

Why do people like bad books? Some of them probably don’t read enough to know the difference. But all the same, I suspect that they wouldn’t be equally content with Martin Amis’ “The Pregnant Widow” should the bookstore clerk have mistakenly slipped that into their shopping bag instead of “The Lost Symbol.” Chances are, Amis’ strenuously inventive prose would strike them as too much work. The popular species of bad writing (for there are many, many kinds of awful prose) abounds in clichés, stock characters and conventional plot twists, and, as Amis indicated in the title of a collection of his literary criticism, he is a general in the War Against Cliché.

Until recently, hardly anyone considered why some readers might actually prefer clichés to finely crafted literary prose. A rare critic who pondered this mystery was C.S. Lewis, who — in a wonderful little book titled “An Experiment in Criticism” — devoted considerable attention to the appeal of bad writing for what he termed the “unliterary” reader. Such a reader, who is interested solely in the consumption of plot, favors the hackneyed phrase over the original

… because it is immediately recognizable. ‘My blood ran cold’ is a hieroglyph of fear. Any attempt, such as a great writer might make, to render this fear concrete in its full particularity, is doubly a chokepear to the unliterary reader. For it offers him what he doesn’t want, and offers it only on the condition of his giving to the words a kind and degree of attention which he does not intend to give. It is like trying to sell him something he has no use for at a price he does not wish to pay.

With the advent of Amazon reader reviews, such readers have finally found a voice, and a vocabulary with which to express their taste. Speed is the operative metaphor. Novels are praised for being a “fast read” and above all for having writing that “flows.” “Flow” is an especially fascinating term because it’s one that literary critics have never used, and it perfectly captures the way that clichéd prose can be gobbled up in chunks at a breakneck pace. “The Da Vinci Code” is over 400 pages long, but you can race through it in about three hours. Combine the large population of casual readers who limit themselves to such books with the hardcore bibliophiles who like an occasional dip into something easy, and you have enough buyers to create a hit.

Lewis also juxtaposed the unliterary reader with what he called the “Stylemonger,” who makes too great a fetish of words and sentences for their own sake. (Persnickety grammar and usage monitors are included in this group.) “He creates in the minds of the unliterary (who have often suffered under him in school) a hatred of the very word ‘style’ and a profound distrust of every book that is said to be well written.” Even if Docx were in a position to lecture his fellow railway travelers as to the superior merits of Proulx and Hollinghurst, he’d run the risk of activating just this sort of resentment, and doing his favorite authors more harm than good.

And, chances are, quite a few of his listeners would be well aware that Larsson and Brown aren’t very good writers. If pressed, they’d say that sometimes they just want to gallop through a story — or in the case of Larsson’s novels, proceed along with a weird methodicalness that taps into what appears to be an amazingly widespread streak of latent obsessive-compulsive disorder. They’d say that they’re not, at the moment, equal to the demands of literature, but that just last week they finished “Disgrace” or “Wolf Hall.” And then they’d say, Would you mind? Are we done here? Because I’d really like to get back to my book.

Referenced in this article:

Edward Docx on why genre fiction is inferior to literary fiction.

Laura Miller on the strange allure of Stieg Larsson’s Millennium Trilogy

Things that annoy Lev Grossman about Stieg Larsson’s fiction.

Conspiracy theory, not characters, made “The Da Vinci Code” the bestselling adult novel of all time. With that novel, Brown, previously a mediocre thriller author laboring in relative obscurity, hit upon the idea of a lifetime. Latching onto a popular but moderately difficult work of pseudohistory titled “Holy Blood, Holy Grail” by Michael Baigent, Richard Leigh and Henry Lincoln (more — much more — about that here), Brown streamlined the authors’ argument that Jesus fathered a dynasty of French kings with Mary Magdalene into an airport page-turner easily understood by people who can barely read. “The Da Vinci Code” is “The Knights Templar for Dummies,” with dashes of remedial art history, travelogues and digs at Christian orthodoxy tossed in to sweeten the brew.

But oh, how to follow it? Once you’ve undermined the doctrine of the world’s largest religion and implied that most of the West’s artistic and scientific geniuses were in on a vast plot, won’t anything else seem a bit of a letdown? The formula has to be just right. Even people who don’t ordinarily go for the obsessive complexities of conspiracy theory liked “The Da Vinci Code” because they saw it as anti-fundamentalist or pro-feminist or even just a way to make the obligatory sightseeing of a European vacation a little more exciting. Plus, as conspiracies go, the Holy Grail theory is easy for the masses to grasp: Light on the history, politics and theology, essentially it’s a sex scandal in the Holy Family.

No wonder it took Brown so long to produce his follow-up, “The Lost Symbol.” He had to find material as portentous, as purportedly earthshaking. It had to be “secret” — otherwise there’d be nothing for Langdon to reveal — and it had to be embedded in the iconography of fine art and architecture, so that the symbologist could triumphantly unmask the coded messages supposedly lurking in familiar masterpieces and monuments to his wondering companions. And lastly, it had to be locatable in a single place, since for all Brown’s rhapsodizing about books as “the oldest and most precious of vessels” in “The Lost Symbol,” his fiction is positively literophobic, frantically translating the quest for knowledge from a search through library stacks into a mad, inane race from statue to church to museum in search of clues. It’s no surprise that Brown, pleading a “short attention span,” delegated the research for “The Da Vinci Code” to his wife, who provided him with summaries of books like “Holy Blood, Holy Grail” so that he didn’t have to actually read them.

Given this list of requirements, what else could Brown pick for his next book but the Freemasons and Washington, D.C.? Masonic rituals are deliberately shrouded in secrecy and esoterica, and Masons number significantly among our nation’s founders (Washington, Jefferson, Franklin, Madison, and so on). Unlike the almost entirely mythical Priory of Sion (keepers of the Grail legacy in “The Da Vinci Code”), the Masons not only exist but are also genuinely fond of sprinkling their motifs (compasses, pyramids, double-headed eagles, the number 33, etc.) in paintings and architectural ornamentation. Washington is home to, among other things, the headquarters of the Scottish Rite, one of the more ritualistically elaborate Masonic bodies, housed in an impressive building complete with 33 pillars and two massive sphinxes.

But while Masonry helpfully supplies much of the necessary paraphernalia of a Dan Brown thriller, it’s short on one key element — a big secret. Yes, Masons must swear never to reveal the details of their rites to outsiders, but by now most sensible people realize these ceremonies consist of little more than grown men playacting with lambskin aprons and bones. Everyone knows Washington was a Mason, that he swore the first presidential oath of office on a Masonic Bible, that the pyramid on the back of the one-dollar bill has some Masonic significance, and so on. Big deal. Only paranoid kooks actually believe that the Masons are devil-worshippers or secretly run the world.

And Dan Brown is no paranoid kook. The Masons are the good guys in “The Lost Symbol,” keepers of the flame, though as with the nonexistent Priory of Sion, you do have to wonder why they bother. It’s hard to see what they have to lose, in this wide-open age, by going public. What they guard is something called “the Ancient Mysteries” and apparently they’ve been at it, in one form or another, for centuries. The Mysteries contain “the spiritual truths taught by the great sages,” according to one aged Mason in “The Lost Symbol,” yet by now even most Masons have forgotten these truths. Only a select inner circle, the 33rd degree of the Scottish Rite, grasps their nature and importance.

I could tell you how Langdon winds up embroiled in a search for these mysteries, which are supposedly concealed someplace in D.C., or about the obligatory freakish and sexually compromised antagonist (a tattooed eunuch) who threatens Everything. I could tell you about the official (an internal affairs muckety-muck from the CIA) who hassles Langdon but is too flagrantly ominous to really be the bad guy, or the shocking climactic reveal about the antagonist’s motivations that any intelligent reader will see coming a mile away. I could describe the various chase scenes, which do demonstrate considerable improvement in craft over “The Da Vinci Code.” But why bother?

The allure of “The Da Vinci Code” lies not in these rudimentary thriller conventions, but in the gradual revelation of the Grail conspiracy theory as the chases and unmaskings and double-crossings play out. The earlier novel’s core secret really is startling to those who haven’t heard about it before. Brown proposes a provable alternative history in which the claims of religious authorities are entirely overthrown, and even if that proposal is based on poppycock, the very suggestion strikes many readers as a breath of fresh air.

By contrast, the same readers are likely to find the enigmas at the heart of “The Lost Symbol” disappointingly abstract and familiar. Brown does try to freshen them up by linking them to cutting-edge science. The academic babe Langdon teams up with this time around, Katherine Solomon, is a practitioner of “Noetics,” a New Age field seeking to prove that thoughts can, in and of themselves, change the physical world. Supposedly she has “created beautifully symmetrical ice crystals by sending loving thoughts to a glass of water as it froze.” These activities and the “shocking new data” supposedly resulting from them are, she hopes, illustrating “the missing link between modern science and ancient mysticism.” Katherine’s work, conducted surreptitiously in a deserted sector of the Smithsonian Institute, is on the verge of demonstrating that the Ancient Mysteries are scientifically sound — a prospect the tattooed maniac (for reasons not entirely clear) regards as catastrophic.

Much of this nonsense will be familiar to anyone who has seen the film “What the Bleep Do We Know?” or read the work of a journalist named Lynne Taggart. Both insist that recent discoveries in quantum mechanics somehow indicate that “consciousness” can effect changes in the material world — claims that actual physicists indignantly dismiss. Katherine is supposed to have evidence proving the power of prayer and the existence of the soul, “Scientifically. Conclusively.” (Brown is big on one-word sentences when he wants to be forceful.) But in this she is only playing catch-up with “the ancient mystics” whose works the Freemasons have hitherto concealed because their insights are “far too potent and dangerous for the uninitiated.”

The exact nature of these insights and why nobody ever used them to make life in the ancient world a little less brief and brutal remains frustratingly vague. Where pseudohistory like “Holy Blood, Holy Grail” bombards readers with too much detail in order to spin an aura of credibility, pseudoscience prefers to throw some authoritative-sounding terms around and then quickly move on before you get suspicious. We’re meant to think that Katherine or Robert or the various Masonic poohbahs they encounter could explain how to defy the laws of gravity and cure rabies with the power of positive thinking if they had a bit more time, but they’re too busy being stalked by black helicopters or surviving an ordeal called Total Liquid Ventilation to get to that at the moment. In the meantime, surely the fact that Isaac Newton was “deep into numerology, prophecy and astrology” should suffice to prove how legitimate such studies are, right?

Still, it’s not as if the preposterousness of “The Da Vinci Code” has put off many readers. If the mystery at the center of “The Lost Symbol” never quite gets solved, it’s still surrounded with exactly the kind of feel-good folderol that readers love in a bestseller. From “The Celestine Prophecy” to “The Prayer of Jabez” to “The Secret,” no one has ever gone broke telling Americans that they can have whatever they want if they only think sufficiently happy thoughts. In fact, pseudoscience could turn out to be even more profitable for Dan Brown than pseudohistory. It may not make for as good a story, but then again, that may be just one more thing that nobody cares about anymore.

In between shots of somber religious statuary and fake Vatican backdrops — shut out of the Vatican, Howard and his crew instead decamped to the racetrack at Hollywood Park, where they re-created St. Peter’s Square and Piazza Navona with a reasonable amount of verisimilitude — there’s lots and lots of talking as Langdon follows clue after clue after clue, hot on the Illuminati’s trail. Luckily, he has a beautiful Italian scientist, Vittoria (Ayelet Zurer), around to assist him. This is important, because much of the plot of  “Angels & Demons” unfolds in the dialog. For instance, Langdon will hold up an ancient book whose cover might be emblazoned with a title like “Libri of Scientia” in fancy letters, and Vittoria will exclaim helpfully, “My God — that’s the Book of Knowledge!” Howard may be hoping that if every narrative detail is repeated for the hard of hearing, the plot will actually end up making sense.

Fat chance. The script, by David Koepp and Akiva Goldsman, wanders around listlessly — no one seems to know where the story is ultimately headed, least of all the writers. They certainly have packed a lot of stuff into “Angels & Demons,” and the whole crazy tapestry might come off as rich and complex if you didn’t think too hard about it. There are plenty of possible bad guys floating around to keep us guessing: Armin Mueller-Stael shows up, scowling, in full-on cardinal garb — you know he’s just got to be up to no good. And Ewan McGregor plays the Camerlengo, a priest who’s entrusted with very important duties at the Vatican, like flying a helicopter — you never know when that’s going to come in handy.

The action unfolds against constant narration: When a character indicates, in a parched whisper, that Langdon should get over to Castel Sant’Angelo fast, he hippity-hops on his way, but not before exclaiming, “The Castle of the Angel!” Every revelation in “Angels & Demons” has a “Colonel Mustard in the library with the candlestick” vibe. Whenever something bad is about to happen, Hans Zimmer’s score flares up like a bad case of stigmata. On the plus side, cinematographer Salvatore Totino does give the movie an aura of ominous pageantry, which is probably pretty hard to pull off at Hollywood Park.

There are a number of grisly details in “Angels & Demons”: As the movie opens, the pope has just died, and the cardinals have gathered to vote on his replacement. The most promising candidates, the top pope hopefuls, are known as the Preferati, and the Illuminati baddies have kidnapped them with the intention of sending each one to a gruesome end. If William Castle had made “Angels & Demons,” he might have opened the movie with the disclaimer, “No one will be admitted during the terrifying Pope on a Rope scene!” Except there is no pope on a rope in “Angels & Demons” — I made that up, with the help of Father Guido Sarducci, aka comedian Don Novello. Come to think of it, why wasn’t he enlisted to adapt this hunk of hokum? That would be hunkus of hokumus in the original Latin.