"I've never searched for controversy," claims Bret Easton Ellis; "it's not something I'm interested in generating." Maybe not, but in the 25 years since his precocious literary debut as a member of the so-called Brat Pack, it has certainly followed him. The author of five previous novels (Less Than Zero, The Rules of Attraction, American Psycho, Glamorama and Lunar Park) and a collection of stories (The Informers), Ellis has been attacked for his flattened, minimalist early style, his later darkly comic excesses, and above all his subject matter: money, sex, drugs, celebrity and violence.

Top of this list is violence. American Psycho, which recounts a New York investment banker's secret life of rape, torture, murder, cannibalism and necrophilia, was notoriously withdrawn by Simon & Schuster before being published by Vintage. In some countries it is deemed so potentially disturbing that it can only be sold shrink-wrapped. At the same time, critics rave about it, academics revel in its transgressive and postmodern qualities, and for all the angry charges of misogyny, it has prominent female defenders, including Fay Weldon, who called it "beautiful, careful, important" and (no arguing with this one) "seminal". Ellis's infiltration of popular culture extends from Eminem songs to video games to references in The Simpsons. Three of his major works to date have received the homage of film versions, with a fourth adaptation (of Lunar Park) due for release in 2011. It seems a foregone conclusion that there will also be a movie of Ellis's much-talked about new novel, Imperial Bedrooms.

Ellis has a habit of resurrecting characters he has used before, but Imperial Bedrooms goes a step further than usual by reprising the stories of a complete group  the alienated teenagers from Less Than Zero, now in middle age: Clay, former college student and now scriptwriter; his old girlfriend Blair, now married; Julian, rent boy turned pimp; and Rip, now, as then, a drug dealer. Less Than Zero opened with Clay coming home to LA from college in New England for Christmas and getting drawn into a downward spiral of drink, drugs, sex and parties, with abuse and violence lurking in  and sometimes emerging from  the shadows. Imperial Bedrooms uses the same device of a seasonal homecoming, this time from New York, and again presents Clay's Hollywood milieu as the antithesis of home. His apartment is stylish but unsafe, and the people he consorts with are beautiful and dangerous, screwing one another in all senses of the word.

The plot, such as it is, revolves around cut-throat casting competition for a film Clay has written, but this is really only a hook on which to hang a dark story about power and perversion  a snuff novel about the living dead in Hollywood. There are masked monsters and hooded victims, knives, needles, filmed executions. A forensic stylist, Ellis documents atrocity unsparingly (there is one scene even his longstanding editor wanted to take out), and while he can write lyrically about Christmas lights and swimming pools and views of Los Angeles enveloped in mist, he is always best when describing damage of some kind, as in this portrait of a drug dealer's features after plastic surgery:

"I don't recognise Rip at first. His face is unnaturally smooth, redone in such a way that the eyes are shocked open with perpetual surprise; it's a face mimicking a face, and it looks agonised. The lips are too thick. The skin's orange. The hair is dyed yellow and carefully gelled. He looks like he's been quickly dipped in acid; things fell off, skin was removed. It's almost defiantly grotesque."

Imperial Bedrooms itself is almost defiantly appalling and sickening, but it is also brilliantly written and coolly self-aware. Clay's psychiatrist, on the brink of terminating their relationship, brandishes his mobile phone  an ever-present prop in this story  "like it's a warning of some kind". Text messages, emails, computer disks and websites alert characters to the fates others have suffered and the danger they are in. Vehicles prowl in rearview mirrors, clues are left in Clay's apartment to signal that he is being watched, and the thug assigned to follow him does it blatantly, "[as] if he were holding a hundred balloons". An epigraph from Raymond Chandler invites comparison between the two writers; there are shades here of Chandler's story "Goldfish", in which someone dies under torture with a hot iron. Imperial Bedrooms has a thriller's pace and structure, drawing momentum from our desire to find out who is behind the hideous mutilation of a body displayed a few pages in.

At the same time, like it or not, the novel dabbles in philosophical waters. The thriller-style hints and foreshadowings also form part of a metaphysical investigation. Here, as in Less Than Zero, Ellis is plumbing the depths of human nature, exposing it at its worst. His writing is existentialist to the extent that it confronts the minimal limits of identity. What does it take for a person to become subhuman, to die inside  for the self to disappear? Answering this question involves believing the evidence in front of you. A lesson to be learned equally by characters and readers (driven home by a pattern of facial references) is to take people at face value. Past actions hold the key to future behaviour: "You have a history of this, don't you?", a member of Clay's circle comments. Forget change, growth, self-reinvention: in Ellis's LA jungle the leopards never change their spots.

Ellis's fellow "brats" Jay McInerney and Tama Janowitz, never as extreme as he was, have since gravitated towards fiction with an openly ethical agenda. McInerney's post-9/11 novel, The Good Life, is explicitly concerned with moral renovation in the context of national crisis, and Janowitz's futuristic They Is Us, subtitled A Cautionary Horror Story, is a dystopian fantasy about the eventual consequences of American shortsightedness and self-interest. Ostensibly, Ellis is resistant to such conversions. In ironically knowing vein, Imperial Bedrooms mocks the expectation that the enfants terribles of the 1980s  narrator and author alike  will have grown up more responsible. In fact the reverse seems true of Clay, who looks younger than his years and has sunk deeper into delinquency during adulthood. Ellis, for his part, still writes like a 21-year-old  in first-person, present-tense narrative and long, hyperconjoined sentences.

The tone is less deadpan now, and Ellis has more of a taste for pathetic fallacy, but he still shows us Clay's life as if on a movie screen, focusing on the set, the props, the sequences of actions.

Even so, underneath the surface of this novel, something political may be going on. The title Imperial Bedrooms is borrowed from Elvis Costello (as was Less Than Zero), but it could also carry a subtext concerning US neo-imperialism. And the silhouette of a devil on the book cover might  just  be linking the image of America as the Great Satan to the characters' diabolical sexual exploits. (In one of the few glimpses of a world beyond southern California a mosque is seen burning on CNN.)

Exploitation, not opportunity, is the watchword among the creeps who run Ellis's Hollywood. Anonymous Hispanic and Mexican boys and girls are used and eliminated off stage with atrocious unconcern, and capitalism permits the rich to purchase the poor and subject them to the vilest imaginable degradations. Do the rapes and murders in this novel stand for America's political and economic relations with non-western countries? Perhaps. Ellis has always (enjoying the paradox) styled himself a moralist, so is he trying to teach us something? Possibly. "You should be more compassionate," one of Clay's girlfriends says, "in the darkness of his bedroom". There may be a moral there. At a pinch.

Alison Kelly is an associate fellow of the Rothermere American Institute, University of Oxford

Graham Greene liked to claim that he had once entered a magazine competition inviting Greenian parodies and finished second. And you suspect that, if the Guardian's John Crace happened to be incapacitated while writing a spoof of Bret Easton Ellis's Imperial Bedrooms, the novelist himself could easily step in, although the result might be considered a little self-conscious.

Certainly, few writers can have combined such distinctive literary mannerisms with such a strong awareness of their own effects. And, in his latest work of fiction, the sense of signature is increased by the fact that the book is a return to an earlier world: Imperial Bedrooms, his seventh novel, is a sequel, quarter of a century on, to his bravura 1985 debut, Less than Zero.

The tone of Less Than Zero was a zombified monologue, in which the narrator, a young, rich brat called Clay, described encounters with sex, drugs and violence in an affectless present-tense: "I'm sitting in my pyschiatrist's office the next day, coming off from coke, sneezing blood." This was a voice so strange and strong  depravities recited in the manner of a shopping list  that it immediately invited pastiche, some of it by Easton Ellis himself, who took casual amorality perhaps as far as it could go in American Psycho, an apologia by a serial killer which the original publisher declined to print.

In Imperial Bedrooms, Clay has doubled in age but voice-recognition software would have little trouble picking up his tense present: "We sit in my office naked, buzzed on champagne, while she shows me pics from a Calvin Klein show." He occasionally seems, though, to have developed the syntactical ability to look back: "They had made a movie about us," the book begins.

That opening mention of a cinematic version of the characters reminds us that Less Than Zero has been a movie and is an example of the energetic self-reference that has become increasingly a feature of this writer's fiction. Lunar Park, his previous book, was an extraordinary mock-memoir in the form of a novel, in which a drug-addled, bisexual American author called Bret Easton Ellis found himself being stalked by Patrick Bateman, the killer from American Psycho. That was not the only realistic/impossible detail, Easton Ellis's work being a form of striptease that sometimes involves garments being put on.

The invitation to read the author into the protagonist of Less Than Zero and now its sequel is strong because, in addition to the first-person narration, Clay is deliberately a blank, a receptor for impressions of those around him. The narrative of Imperial Bedrooms more or less exactly mirrors that of the original  Clay goes to Los Angeles from New York for a passively hedonistic Christmas, although he now possesses not only money but a sort of influence, having become an outwardly successful screenwriter. But, as Easton Ellis's readership will immediately know, writers in Hollywood have no real power, being the playthings of producers. Clay is having frequent sex, fuelled by booze and junk, with an aspiring actress who calls herself Rain, whom he met at the first audition for a movie he's written and who seems to be hoping, by acquiescing to his pleasures, for a call-back to a second reading.

Clay, though, does not seem to be in control of his own storyline: a stalker, whom we suspect has read Lunar Park, keeps sending him menacing texts in italics, mainly variations on "I'm watching you". The major additions to Less Than Zero are technological: the novel is dotted with texts and a character who goes missing appears to have been killed in an "execution video" on the web, although the link proves impossible to activate, leaving only "people on various blogs debating the video's 'authenticity'." The novelist is a laureate of paranoia ("ominous" is a favourite adjective), which usually proves to be justified, as it does here, in a climactic scene of sex and violence which suggests that self-censorship has not been a consequence of the American Psycho scandal.

In terms of American literary inheritance, Easton Ellis adds the playful self-advertisements of Philip Roth to the ambiguously complicit social reportage of F Scott Fitzgerald. Imperial Bedrooms ranks with his best exercises in the latter register, teeming with sharp details of a narcissistic generation: the "spray-on tans and the teeth stained white", "the AA meetings on Robertson and Melrose, the twenty-dollar margharitas from room service", "young girls walk by in a trance holding yoga mats".

Most tellingly, Rip, the young kids' drug dealer in the first book, is still offering the service now, although they fail to recognise him, not because of ageing but his cosmetic attempts to avoid it: "It's a face mimicking a face . . . he looks like he's been quickly dipped in acid; things fell off, skin was removed."

Thankfully, Easton Ellis's literary face-lift to his youthful first appearance has been conducted more subtly, retaining what was initially attractive with a few tight injections of modernity. May the 2035 publication lists include a report on Clay in the third age, when he might need someone to do the sex, drugs and paranoia for him.

Mark Lawson's Enough Is Enough is published by Picador.