Artist of his floating world

Outside, the first spring of the 21st century gilds the improbably spruce and well-tended gardens of Golders Green with daffodils and forsythia. Inside the cool white-painted house of the neat black-clad novelist, Kazuo Ishiguro's imagination is still inhabiting a darker time and place. His fifth novel, When We Were Orphans (Faber & Faber, £16.99), sends a pukka English detective straight out of the prewar whodunnit to Shanghai in 1937 - an unearthly, dissolving city on the brink of total war. There, the oddly plodding Christopher Banks searches in vain for the parents who went missing during his expat childhood, a quarter of a century before. "We think," explains Ishiguro, glossing that logic of the loner's quest for reparation, which recurs throughout his work, "that if we can only put something right that went a bit awry, then our lives would be healed and the world would be healed".

A decade after The Remains of the Day created the immortal Mr Stevens, who declined to object to Fascism because that would breach the butler's code, Ishiguro has not yet done with Second World War - or with the global delirium that foreshadowed it. Hardly surprising, retort a legion of psycho-critics, for a writer born in Nagasaki to a mother who survived the bomb that flattened half the city on 9 August 1945. They will also wish to know the slice of family history that underpins his new portrayal of Shanghai's international community - a brittle bourgeois island in a sea of tumult.

Ishiguro's father was born in that fragile enclave, "and actually lived through this period". It was the place where, at the time, Toyota (then a textile firm) employed the novelist's beloved, samurai-descended grandfather, "the person who acted as father-figure for the first four years of my life in Japan".

It's alarmingly easy for any profile of Ishiguro to descend into a soupy sort of East-West family romance. Formative as the dynastic shifts from Shanghai and Nagasaki to Guildford and Golders Green certainly were, this fixation short-changes Ishiguro the artist and slights the singularity of his take on the savage era depicted in his fiction. (Even The Unconsoled, although notoriously set in some Kafkaesque never-never-land of Mitteleuropa, had a curiously prewar feel to it.)

Last autumn, for example, Ishiguro visted Auschwitz. The insane bureaucratic pedantry of the Holocaust still seems to be preying on his mind. Why did the Nazis divert all these resources into industrial slaughter when "the various fronts were crumbling?" he asks. "It doesn't make any sense in military terms." Even genocide, it appears, can acquire its own mindless momentum, as automatic as a detective's scene-of-crime routine or a butler's morning round.

"It's tempting to say that there was evil man called Hitler who decided to kill the Jews," he comments, but to do so obscures "that sense of the darkest passages of our last century's history coming out of just mayhem and chaos and blood-lust".

As a faithful disciple of the "Golden Age" investigative school of Agatha Christie or Dorothy L Sayers, Christopher believes in the evil-genius theory of crime and disorder. Nail the culprit, and peace reigns again. Yet these cosy conventions evolved, as Ishiguro notes, in the wake of the carnage of 1914-18. "It seemed to me quite poignant that this genre should have flourished as a kind of therapeutic reaction to the horrors of the Great War."

Christopher's progress through the shell-blasted tenements of Shanghai puts paid, at length, to the delusion that the tears of the world can be wiped away with a triumphant squawk of "It was Colonel Mustard, with the lead piping, in the conservatory!" And this surreal mismatch between the society sleuth's myopic mind and the oceanic misery around him - "using a magnifying glass to look at corpses in a war-zone," as his creator says - effectively stops the hero from achieving much of an adult inner life until the book's final pages. "My great vocation got in the way of quite a lot, all in all," reflects the older Banks, in a classic Ishiguro line.

As did, of course, the sacred self-imposed mission of the pianist Ryder in The Unconsoled, of Mr Stevens, and the artist Ono, in his floating world. In this light, When We Were Orphans may prompt some readers to take a premature leap into allegory - it's all a fable of the writer's life, trumpeted Tom Paulin on BBC2's Review programme. The author, more modestly, hopes "people will just enjoy the story". Indeed, he's "not terribly keen on readings that suggest my books are about writing. I've never been interested in postmodernism in that sense."

The new novel offers many more direct pleasures. Its precise but strangely weightless prose glides silkily between the child's-eye Shanghai of the 1910s, the wing-collared pomposity of 1930s London and the chaos of semi-colonial China. The dénouement delivers a storm of revelations, as Banks joins Stevens and Ono as an Ishiguro hero who "has unwittingly rested his life, and what he would consider his laurels, on things he would despise - that's been in my work for a long time."

What Christopher never does, in any detail, is close a case. Mostly, this detective simply doesn't detect. Yet, in the first draft, he certainly did: Ishiguro devised a Golden Age story-within-a-story to show the sleuth in cracking form. Then he "threw away about 110 finished pages". It was "the first time that I've got that far into a book, and then abandoned a whole chunk of it". In contrast, The Remains of the Day went exactly according to plan. ("I used to be quite a controlled writer.")

His problem was the the pasteboard figures wheeled on "simply to be suspects" in a traditional whodunnit could never co-exist with more solid characters. In the end, the pastiche guilty-vicarage subplot dwindled to couple of pages. Finally, perhaps, the great detective never clears up a crime because he enters a modern universe where evil has a systemic, not specific, root. "That's the trouble with overrating Hitler," Ishiguro remarked later. "He turns into Professor Moriarty."

Christopher's quixotic bid to rescue his parents unveils no Napoleon of Crime skulking in the alleys of Shanghai (not even the local warlord, who takes a hand in the plot). Instead, the metropolis collapses into a labyrinth of loss and confusion, symbolised in a bravura passage by a trek through a maze of shell-shattered slums. This section displays all of Ishiguro's uncanny gift for blending fact and fantasy into a seamless, hallucinatory whole. Those close-packed rookeries really existed, and did hold up the advancing Japanese. In Ishiguro's hands, they morph into a dreamscape worthy of Borges.

The author "paid a large amount of money to antiquarian bookshops" for works about old Shanghai. Yet, "ultimately, I'm not interested in solid historical reconstruction". The fictive city comes from him alone. He refused even to open J G Ballard's Shanghai-set Empire of the Sun: "I thought, well, if I read that, I'm going to get sucked into his world." And he has never visited modern Shanghai.

After five novels, the country we might call "Ishiguria" now sports its own unique co-ordinates - a queasy terrain of memory and menace, dream and displacement, as distinctive in its way as "Greeneland" ever was. His sixth book will extend its frontiers. He plans to take a European songwriter from the accursed Europe of the Thirties to the schmaltzy, witty, glitzy heart of American showbiz in its golden age. Ishiguro, who once nurtured dreams of songwriting stardom himself, is drawn to "this very interesting mix of conservatoire-trained, often Jewish, Europeans coming to America and trying to find a new identity".

He'd like to be hard at work on this book now, but the predatory demands of a global publicity circus will keep him from his desk: "The rhythm of publication probably means that I'll settle down to it next spring." Selling your book, he complains, has mushroomed into a "second job" that curtails the lifetime output of authors. "It is both a good thing and a bad thing that the literary novelist now has to account for himself in front of the mass market." The Unconsoled dwells, of course, on the slow-burning panic of the itinerant performer. Its author jokes that it "could be seen to be about the third week of an American tour".

Besides, this youthful 45-year-old worries that his time may be running out. "Novelists reach their peak," he frets, "between 35 and 45, a few years after footballers do."

He scarcely needs to bother about relegation yet. When We Were Orphans discloses a writer not only near the height of his powers but, thanks to its inimitably out-of-kilter vision, in a league all of his own. So "Ish" ends up competing with himself, glumly reeling off the age at which the titans hit their peak: Faulkner in his thirties, Joyce, with Ulysses, at 40; Tolstoy, in War and Peace, at 41... "You suddenly realise, especially when you're no longer young, that you have only a finite number of books."

Surely there's no need to sound quite so... unconsoled? What about the spectacular comeback of Philip Roth, with his string of explosive masterworks after the age of 60? "I must say I find that very encouraging," he replies. And I suspect it will be quite a while before the weeds begin to grow in Ishiguria.