The phenomenal success of David Foster Wallace, Jonathan Franzen and Donna Tartt tempts us to believe that readers of literary fiction crave long novels, but that bit of magical thinking works only for long novels that succeed. After all, Bob Shacochis’s spectacular “Woman Who Lost Her Soul” had 715 pages and was a finalist for the Pulitzer Prize, but how many people actually read it? A few months ago, our reviewer called William T. Vollmann’s 1,356-page novel, “The Dying Grass,” a brilliant masterpiece, but it never climbed onto the bestseller list. The frustrating truth is, readers stampede toward good novels that are very long, except when they don’t, and anyone who can tell you why could make more money selling diet aids and New York bridges.

This debate about the currency of Big Novels is about to get a big boost. The “it” book this fall is “City on Fire ,” a 911-page debut by an unknown writer named Garth Risk Hallberg. Yes, Risk is literally his middle name, but it’s his publisher who’s taking a chance here. Having reportedly paid nearly $2 million for the manuscript, Knopf must be praying that “City on Fire” is worth its weight in Goldfinch. Such irrational exuberance can’t buy a spot on the bestseller list, but it can guarantee coverage. So prepare yourself for what passes for a book publicity juggernaut: Over the next few weeks, you’ll read about this novel everywhere, and you’ll hear the young author interviewed on NPR, and you’ll see pyramids of “City on Fire” at your local bookstore. And at some point, you’ll wonder, “Should I read this novel — or three others?”

That decision may hinge on your stamina, but “City on Fire” is an extraordinary performance. Radiating youthful bravado that will make older authors sniff with contempt (or sweat with envy), Hallberg has conjured what he calls the “muchness” of New York City in the late 1970s. He calculates “the sum of thousands of variations, all jockeying for the same spot.” Like Tom Wolfe — but with less nervous energy and more stylistic elegance — Hallberg climbs quickly up and down the economic ladder. He inhabits the minds of whites and blacks, men and women, old and young, gay and straight with equal fidelity. For almost a thousand pages, he swirls around a single tragedy, sweeping up a vast collection of tangential characters and making every one of them thrum with real life until the lightning strikes, the electric grid overloads, and the city goes mad on that dark summer night in 1977.

Although Hallberg was born in Louisiana and grew up in North Carolina just after this febrile period of New York history, his confident narrative gives the impression that he once shrieked in that punk scene, mainlined those street drugs, invested millions in real estate, thrilled in Penn Station’s bathroom stalls, and strutted down those near-bankrupt avenues when “budget cuts and crime and unemployment had brutalized the city, and you could feel on the street this sense of soured anarchy, of failed Utopia.”

Author Garth Risk Hallberg. (Mark Vessey/Knopf)

Although it’s no more a mystery novel than “Moby-Dick” is a fishing tale, “City on Fire” does revolve around an unsolved shooting, and it offers up a trove of intentionally disordered clues. (Producer Scott Rudin bought the movie rights two years ago.) You’ll want to swallow this story in great chunks. Indeed, you’ll need to — otherwise, you won’t notice, for instance, that the broken “l” key on the typewriter described on Page 457 is used to type the note reproduced on Page 604 — and scores of other illuminating markers strewn around these chapters.

At the center of all this clamoring life is Samantha Cicciaro, a college freshman too cool for her own good. She’s a fan of the briefly super-hip group Ex Post Facto, one of whose songs gives the novel its title. Samantha fell in with those culty musicians and produced a few issues of her own cacophonous zine before being gunned down in Central Park, another victim in a city already terrorized by the Son of Sam. While she lies in a coma in the hospital, Hallberg ventures out into the vast matrix of her friends, cohorts and avengers.

Indeed, “City on Fire” is a novel that never met a character it didn’t like. When we’re introduced to Samantha’s grieving father, we learn all about his failing business as a fireworks operator, which intrigues an affable magazine writer who once slept with a flight attendant who got pregnant and moved to Florida and had a baby. But forget that baby — we’ve got to get back to wounded Samantha, who was dating an asthmatic teenager (one of the novel’s most endearing characters) who is grieving the death of his father and wishing he were even half as cool as Samantha. The night of their big date, her body is found in Central Park by a gay black man named Mercer, who teaches at a ritzy school for girls. He’s just learned that his artistic boyfriend is probably a heroin addict and is definitely the long-lost son of the Hamilton-Sweeneys, a terrifically wealthy New York family. But nobody knows — yet — that the Hamilton-Sweeneys’ business is being slowly taken over by a vampiric brother-in-law whose idea of real estate development starts with a can of gasoline.

Hallberg’s opus depends on its accelerating velocity, its hairpin turns down every side street. There’s something frightening — if not a little ludicrous — about a plot of such intricacy. I picture the walls of Hallberg’s New York apartment so covered with pushpins that they distort the Earth’s magnetic field. The central miracle of “City on Fire” may be that it re-creates this impossibly complex metropolis while also suggesting that everyone in it is more closely connected than the guests around Kevin Bacon’s Thanksgiving table.

And what endlessly fascinating characters they are! Mercer, for one, allows Hallberg to explore the fluid position of gay African Americans at a moment of radical change. He also happens to be a struggling writer whose “chief weakness as a novelist heretofore had been his inability to keep pace with the complexity of real life” — a problem Hallberg does not share.

Mercer’s lover, William, the alienated scion of the Hamilton-Sweeney clan, gives the story access to both the rad art scene bubbling up from the streets and the glitzy world of privileged New Yorkers, which Hallberg treats with a refreshing lack of satirical edge or Fitzgeraldian romance. The very rich may be different from you and me, but in this novel’s sensitive treatment, their advantages dissolve in the same river of human experience that is sweeping us all along. William’s sister, the attractive daughter of the real estate mogul, can rely on trust funds and uniformed servants, but she still feels overwhelmed by self-doubt and mourns the breakup of her marriage and makes us feel her panic when her children go missing on the night of New York City’s blackout.

Aside from its intricate flashbacks, the bursting plot is further enriched by a number of fully reproduced ancillary documents, such as a reporter’s manuscript replete with coffee-cup stains, and an issue of Samantha’s pasted-up zine that offers “some proof that for a hot minute life and art had come close enough to touch.” This “extra” material never feels gimmicky, and it’s certainly not extraneous; in fact, it provides some necessary relief from Hallberg’s onrushing narrative.

Which raises an uncomfortable fact: “City on Fire” burns brightest when it gets fresh fuel. The original manuscript was reportedly much longer, but there are still at least 200 pages of unnecessary flashback and explanatory detail here. Plus, Hallberg’s storytelling is usually so smart that its dim patches grate on the reader. The police work runs dangerously close to TV cliches. And the financial dynamics underpinning a major branch of the plot are fuzzy and melodramatic. “City on Fire” should have sported the kind of monetary knowledge that infuses Adam Haslett’s “Union Atlantic” or John Lanchester’s “Capital.”

But such objections will be drowned out by the vibrancy of a novel whose Whitmanesque arms embrace an entire city of lovers and strivers, saints and killers. Possibly only Mercer — a transplant from Georgia — understands what’s at stake. While struggling to keep his job and his boyfriend, he can’t stop thinking about a novel he wants to write: “In his head, the book kept growing and growing in length and complexity, almost as if it had taken on the burden of supplanting real life, rather than evoking it. But how was it possible for a book to be as big as life?”

“City on Fire” is Hallberg’s dazzling answer to that question.

Ron Charles is the editor of Book World. You can follow him on Twitter @RonCharles.

On Oct. 14 at 7 p.m., Garth Risk Hallberg will be at Politics & Prose Bookstore, 5015 Connecticut Ave. NW, Washington , DC.

City on Fire

By Garth Risk Hallberg

Knopf. 911 pp. $30