The lives of certain authors resemble their work in the way dogs are said to resemble their masters: Ernest Hemingway's valourisation of a stoic masculinity that abruptly guttered out when confronted with its own inadequacy; the jolly, indefatigable showmanship of Charles Dickens concealing the long-guarded secret of his relationship with Ellen Ternan. With the contemporary novelist Donna Tartt, there is a faintly unreal quality to her biography, a modern-day fairytale: the bookish child from a small Mississippi town turned literary prodigy, embraced by southern-lit gurus Barry Hannah and Willie Morris in her first year at the University of Mississippi, swept off to the russet-leafed hothouse of Bennington College in Vermont to rub shoulders with embryonic stars such as Bret Easton Ellis and Jonathan Lethem. Then the fabulous book contract at the age of 28, long glossy magazine profiles and a first novel, The Secret History, which became both a bestseller and a cult favourite.

Tartt prefers not to discuss her personal life with the media, insisting that the focus remain on her work, and she has mostly succeeded in keeping it that way. There is no reason to doubt her sincerity in this, but as with other secretive authors, her reticence tends to fuel the mystique rather than stifle it. Chances are Tartt's life, like most writers' lives, is not especially exciting or exotic, but because it is largely unknown, it can be romanticised. There was even, for a while, a rumour that she'd bought her own island and had retired there to stew in writer's block, like a cross between Noël Coward and a James Bond villain – conclusive proof that many people hold wildly overblown notions of how much money can be made from a single book.

As dopey as they are, the stories people make up about Tartt are recognisably third-rate echoes of Tartt novels. The Secret History – with its cast of undergraduate aesthetes swanning around the campus of Hampden College in their bespoke English suits, quoting Xenophon and Dante while harbouring hopeless erotic obsessions with each other – provides an ideal springboard for fan fiction, and Tartt myths are the real-life equivalent of fan fiction. In a 1992 profile of the author for Vanity Fair, James Kaplan wrote, "With her Norma Desmond sunglasses propped on her dark bobbed hair, her striped boy's shirt ... and her ever-present cigarette, she is, somehow, a character of her own fictive creation: a precocious sprite from a Cunard Line cruise ship, circa 1920-something. A Wise Child out of Salinger." Well, not really – in person, Tartt is cordial, vivacious and unaffected – but that's what we want her to be, a larger-than-life product of F Scott Fitzgeraldian self-invention.

Just as it's impossible to talk of Tartt the woman without invoking a fractal-like array of literary references, Tartt's novels, all three of them, are dense with allusions and homages to beloved books. In the first two, the central characters are saturated in, as well as led astray by, reading. The classics students of The Secret History, under the sway of a charismatic though ultimately elusive tutor, decide to recreate a Dionysian rite out of Euripides' The Bacchae in the woods of New England. They succeed, at a fatal cost. What enchants the novel's most ardent fans, who tend to be young or to have first read it in their youth, is the lush, meticulous way in which it mounts the early adult dream of abandoning a received commonplace identity for a more refined and glittering alternative (an alternative that is usually, in its own way, just as received). Nineteen is the age when we believe we can assemble a self out of tastes and that our mundane past can be shucked as easily as we change clothes. The older you are, the sillier that little posse of wannabe Walter Paters in The Secret History appears, but to young readers they often represent an intoxicatingly doomed splendour.

Evelyn Waugh's Brideshead Revisited is manifestly the model for this aspect of The Secret History, but as the story progresses and the narrator, Richard, becomes entangled in the group's effort to cover up a murder, Crime and Punishment takes over. So far, all three of Tartt's novels have featured an extremely leisurely third quarter. In this one, the characters are forever turning up in each other's rooms, shrugging off their tailored overcoats and calling for a drink and a cigarette with a stormy world-weariness that would be frankly comical if they hadn't killed a man. For all the blood on their hands, it's impossible to take them entirely seriously, and it's indicative of the exacting control Tartt maintains over her novels that even as the tension and menace grows, this satirical element persists.

Fabritius's portrait of a goldfinch is central to the novel. Photograph: Francis G Mayer/Corbis

Then there's the little matter of how preposterous it is that these kids would murder anyone. Yet under the spell of Tartt's storytelling, few readers raise an eyebrow. The sort who do, obeying what I'm sure they believe to be the call of a greater rigour, can complain all they like. It will do no good. The critic James Wood, reviewing Tartt's most recent novel, The Goldfinch, for the New Yorker, objected to the book's stagey improbabilities and twists. He likens scenes from The Secret History and The Goldfinch to a similar passage from E Nesbit's children's novel The Treasure Seekers, and charges Tartt with indulging childish desires for fiction in which "the pleasure of theatrical discovery merges with the pleasures of the narrative, and the reader sees with the eyes of the enchanted narrator". For Wood, all this is a deplorable contrivance, "not the disclosure of a meaningful reality but the management of continuous artifice, a proffered tray of delicious narrative revelations". To which millions of readers have said: Yum.

Later in the review, Wood also calls Tartt into question for having her narrator "liken her characters or scenes to cinematic analogues, as if to work off a debt". There are few cinematic references in her first two novels, although the main character of The Little Friend, a ferocious 12-year-old named Harriet Cleve Dufresnes, has a pal who yammers incessantly about the spy movies he's seen. Harriet, by contrast, immerses herself in Robert Louis Stevenson and accounts of the life of Harry Houdini and Captain Scott's expedition to the south pole. Like Nesbit's child characters (or, for that matter, Tom Sawyer), her very cells are infused with tales of adventure and heroism, albeit fairly dated ones. Harriet's heroes are Napoleon and Genghis Khan and Lawrence of Arabia. Growing up in a small town in Mississippi during the 1970s does not present her with many opportunities for derring-do, but "though she could not say exactly what it was she wanted to do, she knew that it was something grand and gloomy and extremely difficult".

Harriet is a highly literary creation, a fusion of Harriet M Welsch from Louise Fitzhugh's New York City-set children's novel, Harriet the Spy (1964), and Mattie Ross, the narrator of Charles Portis's great western novel, True Grit (1968). Although two celebrated adaptations of True Grit have been filmed, Portis remains a writer's writer, not widely known beyond a modest circle of fanatic followers, Tartt among them. (She narrated the audiobook of True Grit in 2006.) Think of him as the missing link between Flannery O'Connor and Elmore Leonard. His Mattie, like Tartt's Harriet, is a being of sheer will, an implacable fury hunting down the perpetrator of a capital crime against her kin. (Mattie seeks her father's killer, while Harriet vows to discover who's responsible for the mysterious death of her older brother at the age of nine.) But the avid reader in Harriet is all Tartt, as is the languid, gooey texture of her small-town southern childhood, surrounded by her grandmother and great aunts, a bevy of genteel, elderly belles.

Harriet is a child assembling herself from books, much in the way the classics students in The Secret History do. Her chum and sometime disciple, Hely, regards her as a "genius" (which is what Morris called Tartt the day they met), and while Hely is a fool, in this respect he's on to something. Harriet has the fixed, intelligent determination of all truly extraordinary individuals. As such, she has no choice but to forge her identity from sources outside her immediate surroundings, and furthermore to do it selectively. "She did not care for children's books in which the children grew up," Tartt writes, "as what growing up entailed, in life as in books, was swift and inexplicable dwindling of character. Out of a clear blue sky, the heroes and heroines abandoned their adventures for some dull sweetheart, got married and had families and generally started acting like a bunch of cows."

The Little Friend is the least popular of Tartt's novels, in large part, I suspect, because it is told in third-person omniscient narration. No doubt Tartt thought Harriet too extreme a personality for a reader to inhabit for 550 pages. Various chapters are told from the points of view of Harriet's relatives, of Hely and of members of the Ratcliff clan, the poor white counterpart to Harriet's Cleve relations, who once owned a plantation house called Tribulation. Two of the grownup Ratcliff brothers – including Danny, who Harriet comes to believe is her brother's killer – cook and sell crystal meth out of a trailer. In recounting their feckless exploits and paranoid ravings, Tartt flexed novelistic muscles she'd barely exercised in The Secret History. No one writes more gorgeously about the transports of recreational drug use. Here's Danny, not yet tweaked out of his mind: "Blue sky, fast music on the radio, long speedy nights that skimmed on and on towards some imaginary vanishing point while he kept his foot hard to the bass and sped right through them, one after the other, dark after light after dark again like skimming through summer rainstorms on a long flat stretch of highway." And then later, when his binge inevitably goes sour: "Around and around turned his mind in the same useless groove, like the doorknob to his bedroom, which turned and turned quite easily without actually opening the door."

Illustration by Paddy Mills.

More than one critic has complained about the improbable Britishisms Tartt puts in her American characters' mouths (in The Goldfinch it's expressions such as "bitter old sod" and "crikey") or instances of noticeably archaic language, such as Richard's exclamation of "Golly!" in The Secret History. These odd touches occur not, as some readers seem to assume, because Tartt doesn't understand the way ordinary people talk. The Ratcliffs, particularly Danny's ranting big brother Farrish, speak an unvarnished southern vernacular ("Somebody ... somebody clumb up there and turned them snakes aloose at Eugene's"). Theo's leathery sexpot of a stepmother in The Goldfinch is spot on, right down to her statements that end with the upward lilt of a question mark. So when characters such as Richard or Theo adopt fusty speech mannerisms or make obscure references (to, say, "an accent like Curt Jurgens in Battle of Britain", a film virtually no American under 50 has ever seen), it's deliberate. That's Tartt's way of establishing that these people have set themselves apart and slightly outside their own time and place.

But to eliminate references to the profane cinema entirely, as Wood seems to demand, would be absurd. Movies are integral to the way real people talk and think. Whatever "meaningful reality" signifies in Wood's mind, individuals who read a lot and who see a lot of films are constantly comparing themselves and the events in their lives to the characters and events in literature and on screen. It works both ways, too; art and life interpenetrate each other. It is Harriet's reading of The Jungle Book that convinces her to try to kill Danny with a poisonous snake, a crazy notion only if you are not a person who patterns her life after adventure yarns. If few of Tartt's readers are like Harriet, plenty of them are variations on the classics students of The Secret History; when people live for culture, they talk about culture a lot and usually try to live it as well.

The Little Friend is a far more convincing, technically accomplished and formally sophisticated novel than The Secret History, but it was less successful at inducing the heady, cloistered mood that the first novel's devotees adored, and so was generally considered a disappointment. (To anyone first coming to The Secret History in middle age, as I did, this is a baffling preference.) The Goldfinch marks Tartt's return to the first-person male narrator, a choice that multiplies the pleasantly askew quality of her fiction. Her male narrators have delicate, melancholy temperaments. They pine for unavailable girls and approach the available ones with no great hunger. They seem uninterested in establishing their place in the usual male pecking order. They register as androgynous rather than masculine, not so much unconvincing as bewitchingly phantasmal, like Shakespeare's cross-dressing heroines, who make much more captivating boys than any real boy could.

In The Goldfinch, Tartt has dispensed with overt literary references. Theo does carry a copy of Antoine de Saint-Exupéry's Wind, Sand and Stars, a gift, on a cross-country journey, but the book is a talisman of a genuine friendship instead of a substitution for one. Rather than have her narrator deliberately emulate fictional characters, Tartt has taken a fistful of Dickens novels, ground them into a fine powder and then blown the results all over her fictional world: Dickens permeates and perfumes The Goldfinch. So does Salinger, at least in the novel's New York passages, but as a flavouring rather than outright citation. The events in The Goldfinch, from the nebulously motivated terrorist bombing of the Metropolitan Museum, in which Theo loses his adored mother, to the devices by which he ends up in secret possession of the Carel Fabritius painting that gives the novel its title, to the climactic showdown with a bunch of international gangsters – all of this is as outlandish, as frankly and unashamedly fictional, as the bacchanal in The Secret History or the scene in The Little Friend where Harriet and Hely succeed in dropping an albino king cobra from a highway overpass into the sunroof of a moving car.

The Secret History's Hampden College is similar in many respects to Bennington College, where Donna Tartt was a student. Photograph: Alamy

Tartt makes you believe all of it, first because most readers want to; anyone game to attempt an 800-page novel is usually someone whose meaningful reality encompasses a good number of fictional experiences, as well as the enveloping pleasure of childhood reading. But stringing a bunch of unlikely adventures together is not enough to seal the deal, or any two-bit pulp writer could pull it off. Tartt marries her narrative fancy to a fully imagined, observed and rendered version of the world. (This was, not incidentally, also Dickens's method.) Her novels famously take about a decade to write and, like a Hollywood blockbuster of which people say you can see every dollar on the screen, with Tartt's writing you see every day on the page. Her prose has the inimitable burnish of hammered silver or hand-rubbed wood. Like the antiques that Theo learns to restore under his apprenticeship to Hobie, the kindly dealer who takes him in, it has "the magic that came from centuries of being touched and used and passed through human hands".

A signature of Tartt's prose style is the evocative list, like this snapshot of a detail from Rembrandt's The Anatomy Lesson appearing in a poster for a Met exhibition: "livid flesh, multiple shades of black, alcoholic-looking surgeons with bloodshot eyes and red noses." The sketch-like quality of this technique invokes the voluminous notebooks Tartt is known to keep, an omnivorous reaping of whatever comes before her eyes, ears and fingertips. In her earlier books these lists can feel undercooked, as if they were lifted directly from a page of jotted impressions; perhaps that's why she's worked more of the descriptive passages in The Goldfinch into full sentences. Still, the items flash before the reader like the half-noticed ephemera we all encounter daily – "we started down toward the crosswalk at 79th Street: past topiaries in baroque planters, ponderous doors laced with ironwork" – nailing down the novel to the material world with every sentence. Tartt's ability to summon up the New York of Holden Caulfield and Holly Golightly is intertwined with her gift for conjuring the New York that is actually there, right now, if you happen to walk down 79th Street yourself.

Finally, The Goldfinch also returns Tartt to the great theme of her work: not the one signalled by her closing paragraph, with its celebration of "the history of people who have loved beautiful things, and looked out for them, and pulled them from the fire", but friendship, that thin, drab word we use for life's great blessing. The friendships at the centre of The Secret History are an alluring phantom; Richard's thwarted longing for them forms that novel's emotional core. And Theo's relationship to Boris – the son of a crooked Russian businessman turned even more crooked himself, and Tartt's most vivid character – is the hook that lodges itself most deeply in the readers of The Goldfinch. It is this friendship, not anyone's devotion to art and its ideals, that saves Fabritius' masterpiece, just as Hobie's friendship, freely offered, rescues the orphaned Theo. A strange gift, this love we feel to people connected to us by neither blood nor mating. It's so improbable. It makes no sense. It is arbitrary and implausible and fabricated out of thin air like a story told to a lonely child. Nothing could be more fantastical, or more real.

• The Goldfinch is out in paperback from Little, Brown on 5 June. The Baileys winner is announced on 4 June.

• This article was amended on 30 May 2014. The earlier version misspelled Ratliff as Ratcliffe.