SPIRITS IN WAITING / BOOKER NOMINATION

FOR a book of such dark brilliance, this third and final novel in Pat Barker's superb exploration of the First World War is conspicuously full of sunlight. Sometimes the sun is a bloody disc, pregnant with apocalyptic threat, but more often it's just the sun, twinkling with democratic indifference on the dead and soon-to-be-dead in the battlefields of France and on pink- skinned non-combatants at the English seaside. Nothing could better suit Barker's incisively ironical vision than that this mad, savage war should climax to the accompaniment of so much delightful weather.

The Ghost Road belongs to William Rivers and Billy Prior, two of the most complex and engaging figures from the earlier novels. Rivers was the real-life neurologist who spent the war treating shell-shocked and wounded British soldiers, when possible rendering them fit enough to have another opportunity to die for England. In Regeneration his star patient was the poet Siegfried Sassoon. Prior is the (wholly fictional) young working-class officer - clever, enthusiastically bisexual - whose battle trauma Rivers tried to cure in The Eye in the Door. In that novel their edgy encounters led to a cautious and ambiguous mutual affection. Now, in the summer of 1918, a patched-up Prior is about to leave for his fourth tour of duty in the trenches.

The novel chiefly alternates between the diaries Prior writes while preparing for one of the last, most self-evidently suicidal British offensives of the campaign, and Rivers's recollections of a pre-war anthropological expeditions to Melanesia. Either of these extended meditations would alone be powerful stuff. In tandem, they echo and illuminate each other in ways that both wrench your heart and make the hairs on the back of your neck stand up. Barker has never tackled her themes - the nature of courage, kindness, cruelty and hypocrisy, what happens to minds at the lonely extremities of experience, what it means to be a man - with more rigour or cogency.

For Prior there is a brief, bucolic interlude in the ruined French countryside before he resumes his dual duties of mothering and brutality at the Front. (One of your men needs a new boot? Take one from a corpse, remembering to scrape out all remnants of the former owner.) Among the seasoned officers, most of them perfectly aware that the war is out of control, there's a terrible weary fatalism. Only the innocent new recruits and the top brass can afford to be sentimental. At a patriotic sing-song, fat, mawkish tears roll down the cheeks of the fearsomely brave and bullish Colonel Marshall- of-the Ten-Wounds, while Prior's new batman, an actor in civilian life, is much given to "once-moring unto the breach at Agincourt during bayonet practice".

The bitter realism of Prior and his peers in no way precludes heroism in battle, or pity either, though the fallen are soon out of mind. When even the living are only "ghosts in the making", you have to "economise on grief".

In London, Rivers tends the other wreckage of the war: the officer whose guilt and horror make him smell putrefaction on his own body, the one whose hysteria - a term the victims resent for its implication of "female" weakness - has paralysed his legs. Briefly feverish with Spanish flu (one of the book's few transparent formal devices), Rivers starts reliving his bizarre, revelatory Eddystone Island experiences.

Frightened but fascinated among people patently itching to get back to their now-banned favourite pastime of head-hunting (it was such fun), Rivers, his protective inhibitions for once peeled away, was privy to the awesome rituals by which the bloodthirsty islanders displayed their parodoxical reverence for life and their easy acceptance of the power of ghosts. They also had a matter-of-fact word for the condition of approaching death, of being beyond help. It's a condition that applies equally to the ghosts-in-waiting in Prior's French dugout and to Hallet, the so-recently idealistic boy now lying in Rivers's hospital with half his head shot away, gargling out a final bleak verdict - on war? on life? - while his doubly uncomprehending family (they are civilians, they can never know) look on appalled.

If this is an uncompromising work, it's far from spare. As in the two earlier books, there is an unwavering commitment to vividly concrete (though never incidental) narrative detail, a lot of sly humour and an inspired and seamless welding of the real and imagined. Wilfred Owen appears memorably and so, in Rivers's recollections of childhood, does Lewis Carroll, a family friend. This famous admirer of little girls adored Rivers's sisters but disliked William and his brother, prompting the offended future student of human nature to stammer out one of the questions that haunts this book: What's wrong with boys?

The Ghost Road is a marvellous novel, not least for its tough, unself- important prose which nevertheless flexes effortlessly to encompass the narrative's many moods and voices. Here for instance is Prior, squaring up to catastrophe not long before the book's quietly stunning end: "Patriotism honour courage vomit vomit vomit ... I look around this cellar with the candles burning on the tables and our linked shadows leaping on the walls, and I realise there's another group of words that still mean something. Little words that trip through sentences unregarded: us, them, we, they, here, there. These are the words of power, and long after we're gone, they'll lie about in the language, like the unexploded grenades in these fields, and any one of them'll take your hand off."