The image of London portrayed in Zadie Smith's fourth novel, NW, reminds me of the way Glasgow was typically depicted for many years: chippy, angry, shifting into a future it wasn't completely comfortable with, leaving behind a certain kind of post-industrial identity it had lived with for so long.

Change isn't easy, as each of the characters who lead the four sections of this novel are forced to acknowledge; change can even be deadly. Change can wipe out an identity.

But as Smith knows, change is also the lifeblood of any city. Put a stop to immigration and a city will die. New faces, new ways and new streams of people flooding in all show that it's a living, breathing creature and one, most importantly, with a future. It says that this city matters in the world, because the world is coming to it. Only, in NW, a part of that living, breathing creature is also a monstrous part. Is that ever-increasing newness part of its monstrousness, or something separate altogether?

In one particularly loaded section, old left-winger Phil Barnes wants to admit multiculturalism into his world view, but struggles, not without humour, to keep up with his younger neighbour, Felix: "'Those girls, man. Tia's just long. Ruby's bare lazy.' 'Your words! Not my words! Let the record show!' said Phil, chuckling, and put his hands up in the air like an innocent man. 'Now let me get this right: "long" means always late, doesn't it? I think you told me that last time. See! No flies on me. I keep up with the slang ...'"

London isn't always kind to who is new; at best it is indifferent. But the people living there needn't be. When the story begins, it is with second-generation Irish Leah Hanwell, confronted by a neighbour who comes crying to her door, begging for help for her mother who's had a heart attack. Leah is kind, she is generous, she shares Phil Barnes's left-wing politics and she gives the crying young woman, Shar, £30 for a taxi to the hospital. Later that night, her Algerian husband, Michel, will scold her for falling for a scam. Shar will never pay the money back, he says. And he is right.

Confrontation is rife in this city. Leah and Michel will face a more violent encounter than simply a neighbour out to make a quick buck, and so will Felix, the reformed drug addict who has been given a second chance with a new woman and a new job as a mechanic. Leah's childhood friend, Natalie, possibly the most complex character in the novel, has moved up in the world with her barrister career and city finance husband, and will join an old woman in the park as they confront a pair of teenagers smoking in a children's play area. Everyone is struggling with the place they occupy; nobody feels sure of it lasting.

Smith mirrors the chippyness and the temporariness of her message in the form of her narrative: sentences are pared back until they jut out, ready to spike you. Links are cut to get rid of any smoothness; words form pictures on the page. Sex is brisk or desperate: the fallen aristocratic actress, Annie, now a soak with a crack habit and only in her mid-forties, although sounding like an 80-year-old, lures Felix with her obviousness. He pulls out her tampon with his teeth in what has to be one of the most grimly comical scenes in the book. Dialogue, too, has this darkly comical feel, as Smith works hard to avoid cliché but also sound naturalistic.

That sense of working hard is a little too strong, in the end. Smith is that increasingly rare thing in mainstream publishing at the moment: a challenging read. For that alone, she should be cherished. But there is too strong a sense of a puppet master or mistress at work here: sentences are just a little too carefully sculpted and polished, lives are just a little too easily led into the path of violence or harm. This is manufactured chaos, choreographed anarchy whose sense of danger, while feeling real, never quite feels real enough.