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A clear frontrunner to be the year's most extraordinary novel, Never Let Me Go is the third book in what could be called Kazuo Ishiguro's Bewilderment Trilogy. Like its predecessors, The Unconsoled (1995) and When We Were Orphans (2000), it is riddled with mystery. As Kathy, a 31-year-old carer living in England in the late 1990s, looks back at her school days at Hailsham, a picturesque establishmentnestling amid quiet countryside, an unsettling strangeness emanates from her reminiscences. What initially seems a near-idyll of benign teachers, lively students, stimulating classes, sporting triumphs on the playing fields, midnight gossips in the dorm and friendly strolls around the pond with its bulrushes and wildfowl assumes an increasingly out-of-true aspect. Innocuous words — "carer", "students", "donations", "complete" — take on deepeningly sinister overtones. Gradually, through Kathy's rosy-tinted retrospect, the contours of a horrific situation loom.

Ishiguro's adroitness in achieving this is masterly. His previous two novels, each featuring a perplexed narrator in a world where it was often also hard for the reader to make out what was going on, seemed somewhat fruitless experiments in low-visibility fiction. Here, the techniques they pioneered come into their own. Once again, terminology such as "baffling", "wasn't clear" and "couldn't fathom" casts a haze over events. Uncertainty signifiers — "maybe", "somehow", "perhaps" — work overtime. Kathy peers through "misted-up" windows and at foggy vistas. The terrain of her recollections is similarly obfuscated ("Your bemusement is perfectly reasonable," her former headmistress assures her late in the story). Attempts to establish facts terminate in culs-de-sac ("Of course, I'll never know for sure", "I don't really understand it"). The closest she gets to the definite are formulations such as "pretty certain" and "almost certainly".

An appetite for the enigmatic has been discernible in Ishiguro's fiction ever since his debut novel A Pale View of Hills (1982), with its eerie hints and intimations. Obliquity has always been his favoured approach to atrocity. His first three books, each featuring a diffident narrator (a widow from bomb-ravaged Nagasaki, an artist damaged by collusion with Japanese militarism, a butler tainted by service to a fascist British aristocrat), comprise a kind of trilogy about the disorientations caused by war.

With his fourth novel, The Unconsoled, a shift occurs. Doubt was central to the earlier books. Now bewilderment becomes paramount. Twice the length of any other Ishiguro novel, this phantasmagoric work pushes a musician on tour in a teasingly unidentifiable European country into a labyrinth of wrong turnings, weird transitions and surreal twists. Amid an air of apparently aimless tricksiness, a story line as frustratingly ingenious as an Escher staircase leads him in bizarrely inconclusive directions. When We Were Orphans, in which a 1930s detective investigates his parents' disappearance in Shanghai (and the world of the whodunit with its neatly solvable quandaries
was juxtaposed with reality's messily intractable problems), continued this fictional strategy. Again overloaded with the inexplicable and improbable, the book seemed ambitious but ultimately abortive.

With Never Let Me Go, Ishiguro brilliantly accomplishes what he was striving towards in those works. Where fantasy from Lewis Carroll to Kafka gave him his blueprint for The Unconsoled, and the golden-age murder mystery tale hovered behind When We Were Orphans, he now selects a scenario that wouldn't be out of place in science fiction, and, against the odds, suffuses it with human warmth and distress.

As Kathy, on the brink of a crucial career change, takes stock of the first three decades of her life, she draws you into absorbed involvement with her story. Although the wider shape of things is indistinct, vivid details abound. Hailsham's rituals and routines are engrossingly re-counted. Like all other Ishiguro narrators, Kathy is impeccably lucid even when — especially when — confronting the cryptic. The prose is scrupulously precise. But there are odd little veerings of mood, sudden brief drops into stoical-sounding melancholy. Passed by quickly in her narrative, vaguely peculiar phrasings and occurrences hook themselves puzzlingly into your mind. Why does the Hailsham syllabus place quite so intense an emphasis on "creativity"? Isn't the cosseting of the students being carried rather too far by almost weekly medical checks? Can it be true that the authorities are so worried about the dangers of smoking that works such as the Sherlock Holmes stories are banned from the library because of their high nicotine content? Aren't people a little overconscious of the dangers of being overheard? Why does free-spoken Miss Lucy leave the school so abruptly?

Curiosity about such matters is adeptly awakened, then deflected. For the foreground of the novel is kept busily occupied with the interactions of Kathy with her best friend Ruth and Tommy, the boy both are attracted to. With his almost nonchalant-seeming skill at creating character, Ishiguro sets a cat's cradle of psychological and emotional tensions quivering between often irritable and irritating Ruth, sturdily decent Tommy with his occasional, unaccounted-for flurries of rage, and sensible, sympathetic Kathy.

What happens among them is enthralling enough but is played out against more and more attention-seizing disclosures of the circumstances inside which they find themselves. Lives maimed by oppressive milieux have been at the heart of almost every Ishiguro novel. Here, he carries this preoccupation a cruel stage further. Exploitation, always an important theme, emerges in a disturbingly macabre form. Graceful and grim, the novel never hardens into anything as clear-cut as allegory but it resonates with disquieting suggestiveness. Slowly uncovering an appalling system, Ishiguro uses it to stir emotions — shock, compassion, shame, guilt — that exposés of brutally callous social or global injustices might evoke. Discomfitingly, he spotlights the out-of-sight-out-of-mind unfeelingness on which human comfort can depend.

Heightening the poignancy, his protagonists here are — like Stevens in The Remains of the Day and the painter Masuji Ono in An Artist of the Floating World (1986) — patient victims, resignedly obedient to what they consider their duty. Understatement is, as always, deployed to great effect. A phrase such as "a bit of bleeding" covers abysses of horror. Tommy's most outspoken outcry against a monstrous status quo is to say twice that "it's a shame".

Not since The Remains of the Day has Ishiguro written about wasted lives with such finely gauged forlornness (like that novel, this one harrowingly concludes with someone weeping on a sea shore). That he contrives to do so in a narrative crawling with creepy frissons is remarkable. Not the least out-of-the-ordinary feature of this novel, with its piercing questions about humanity and humaneness, is the way it affectingly moves past gothic shudders to a wrenchingly desolate ending.

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