Joshua Ferris’s new novel is about a dentist, and like a good dentist, Ferris welcomes us in with a few jokes and some distracting chitchat. By the time we realize what we’re in for, we’re flat on our backs, staring wildly at our own reflection in the goggles of a person we’re not sure we should trust.

If you’re afraid of dentists or demanding fiction, back away because “To Rise Again at a Decent Hour” is a brilliant mess of a novel that drills at a raw nerve of existential dread. It’s a deceptively comic treatment of Emily Dickinson’s claim that “Narcotics cannot still the Tooth/ That nibbles at the soul.” Ferris has managed to blend the clever satire of his first book, “Then We Came to the End,” with the grinding despair of his second, “The Unnamed.” The result is a witty story that chews on Internet scams, relationship killers, crackpot theology, baseball mania and the desperate loneliness of modern life.

Plotting in the traditional sense is not Ferris’s prime interest — or his strongest talent. What matters to him is how characters respond to the approaching darkness. No matter the setting, for Ferris, it’s always Rosencrantz and Guildenstern and the Rest of Us. There’s some complication in this third novel — even some remnants of intrigue — but we’re locked in the endlessly spiraling mind of Paul O’Rourke, D.D.S., a functional depressive with a successful practice in New York City. Peering into the moist maw of one patient after another — seeing the incipient rot, noting the early signs of mortality — has only exacerbated his angst. This is a man who can’t get a puppy because someday it might die; he doesn’t want kids because that would take suicide off the table.

And so he has poured his enthusiasm into one hobby and relationship after another, only to grow bored — or to frighten away the objects of his affection. Even God has proved inadequate to his boundless zeal. “I would have liked to believe in God,” he tells us, but church is just “a place to be bored in” and the Bible offers only “firmament, superlong middle part, Jesus.”

These erratic musings of a “misanthropic and chronically unhappy” man are interrupted one day by a mysterious encounter. “My life didn’t really begin,” Paul tells us, “until several months before the fateful Red Sox summer of 2011.” Someone he doesn’t know well insists on having a tooth extracted without any anesthetic; instead, the patient wants to rely on Tibetan meditation techniques. “I’m not actually here physically,” the man claims. As you might expect, that doesn’t work well, but as the patient leaves, he whispers, “I’m going to Israel. I’m an Ulm, and so are you!”

“To Rise Again at a Decent Hour” by Joshua Ferris (Courtesy of Little, Brown)

That enigmatic remark trips a cascade of strange events, starting with the creation of a nice-looking Web site for Paul’s practice — a Web site that Paul never sanctioned nor requested. If this is identity theft, it seems like the best kind to suffer. But while Paul tries to shut down that unauthorized site, phony Twitter and Facebook accounts using his name start offering comments about the modern-day descendants of Amalek.

If you know the Hebrew Bible, you may recognize the Amalekites as the ancient and eternal enemy of the Jews, but Paul, of course, has never managed to make it past “the barren wives and the kindred wraths and all the rest of it.” Now, however, he’s infected by curiosity about this faux version of himself online, and soon he’s drawn into a labyrinth of Web sites either condemning the Amalekites or celebrating them as an ancient sect of religious doubters who have been unfairly maligned. It’s just the sort of occult, incendiary debate that metastasizes all over the Internet, inflaming anti-Semites, alarming the Anti-Defamation­ League and leaving Paul ever more entangled in the strident, quasi-academic claims of shadowy kooks. While ignoring his patients and frightening his staff, he grows convinced of his own seriousness and sincerity.

The great challenge of creating a manic-depressive narrator is conveying the intensity of his mania without forcing readers to endure the tedium of actual mania. Although Ferris reportedly cut hundreds of pages from “To Rise Again at a Decent Hour,” he has managed to preserve the novel’s meandering gait, the artless, associative jumps and swings of a man flailing about.

There are still long patches of blather; three pages about hand lotion, for instance, exemplify the author’s tendency toward self-indulgence. And some stale jokes about social media addiction should remind everyone that Dave Eggers’s “The Circle” has exhausted that line of satire. But at his best, which is most of the time, Ferris spins Paul’s observations and reflections into passages of flashing comedy that sound like a stand-up theologian suffering a nervous breakdown.

In the novel’s weirdest and most daring sections, Paul describes his longstanding attraction to Judaism, despite his confirmed atheism. Why, he wonders, can’t he join with the community of the faithful without swallowing the demands of belief? If he can’t be Jewish, can he be, say, “Jewish-ish”? In the dark folds of despair, he fails to detect the offensive strains of his desperate ­philo-Semitism. ­

Howard Jacobson explored some of these issues in his equally plotless comic novel “The Finkler Question,” which won the Booker Prize in 2010. Ferris’s book is less polished, but ultimately it’s better for that raggedness — more poignant, more tragic. For all Paul’s ludicrous ravings about the Red Sox and a Lost Tribe and the girlfriends who got away, he’s frightened of something profound and universal. “The day is hard enough. Don’t leave me alone with the night,” he pleads. For all his fleeting affections and loony obsessions, he knows: “What separated the living from one another could be as impenetrable as whatever barrier separated the living from the dead.”

You can rinse now. But you won’t get the taste of this harrowing story out of your mouth.

Charles reviews books every Wednesday in The Washington Post. You can follow him on Twitter @RonCharles.


TO RISE AGAIN AT A DECENT HOUR

By Joshua Ferris

Little, Brown. 337 pp. $26