BOOK REVIEW / How did Emma first kiss Nelson? Discuss: Natasha Walter finds Susan Sontag shrugging off the messiness of fiction in favour of the essay: The Volcano Lover - Susan Sontag: Jonathan Cape, pounds 14.99

IT IS A truth universally acknowledged that great critics rarely write great novels. They are too used to the risk-free market. When it comes to the maelstrom of fiction, they either stay on the edge and write detached taradiddles, like George Steiner or Gilbert Adair, or fall in, losing their cool entirely, and then we are left with the mushy embarrassments of a Michael Ignatieff or Julia Kristeva.

Susan Sontag's earlier fiction scarcely qualified as fiction at all, it was so safe, so detached, and quirky and unengaged. A so-called short story called 'Project for a Trip to China' written in 1978 had paragraphs that ran, complete: 'Consider other possible permutations,' or 'Colonialists collect.' But her new novel, The Volcano Lover, is subtitled 'A Romance', went into the bestseller lists in the United States, and weighs in at more than 400 pages.

Certainly, it is not an embarrassment. Sontag maintains her critical distance throughout. By choosing a historical subject - the lives of Sir William Hamilton, ambassador to Naples and collector of antiquities; his second wife Emma and her lover, Lord Nelson - she can flaunt her learning, and can retreat within the carapace of a critic when things look too dangerous outside. That is very clear in the most difficult section of the narrative, when the three darlings of British and Neapolitan society bring disgrace on their heads by instituting a Terror in Naples as retribution for a republican revolt.

Sontag does not even try to discover on her own terms, on fictional or biographical terms, what their motivations were, what scalding guilt they felt or did not feel. She slips briskly into history-student mode, detached and hanging fire: 'Since they were individuals, claiming to be acting for the public good, one says that they did not know what they were doing. Or that they were dupes. Or that they must have felt guilty after all.'

Even during gentler stretches of narrative, Sontag too often shrugs off the messiness of fiction by sticking with the genre she knows and loves - the essay. William Hamilton becomes a pretext for an essay on collecting; Nelson on being a star; Emma on beauty - 'What do you do with beauty? You admire it, you praise it, you embellish it, you display it; or you conceal it . . .'; elsewhere we get short disquisitions on privilege, on art and horror, whatever. These are invariably intelligent and often funny, but because they are here they are not as closely argued as her actual essays, and because they are here they block the movement of the story, with their very pressing, contemporary tone taking over from the historical novelist's essential methods of mimicry and pastiche.

No one expects Sontag to be Marguerite Yourcenar or Leo Tolstoy or Hermann Broch; but some way of representing the voices of her historical characters has to be found. This is her great problem, which she sidesteps in various clever ways. She uses direct quotations from letters or memoirs. She over-uses that style of excessive clipping and repetition, without proper punctuation, that has become so beloved of clever writers forced to deal with the banal. 'The Cavaliere said it was very tasty. The King said, tell me a story. A story, said the Cavaliere.'

She questions the need for mimicry at all with would-be post- modern yearnings over the impossibility of representation. And she destroys its possibility with fey anachronisms, flip 18th-century references to Darwin and Freud - here is an 'evolutionary overachiever', here a 'sign of repressed rage'.

But from time to time Sontag has to do it - do the party, the inquisition, the sex scene, the letter, the interior monologue. And then she often loses control. It is funny to see how Americans have been conditioned to see the historical past as something lived in translation; here are whole paragraphs so tainted with unEnglish phrasing and expression that they would be thrown back in the face of any student presenting them in an unseen paper: 'Learning the news that same morning,' one classic sentence begins, 'the Cavaliere set out in his best carriage to perform the offering of condolences. Upon entering the palace . . .' Mixed in with these Latinate constructions and stilted dialogues are truly archaic uses - splendorous for splendid; acerb for acerbic - and misuses: Catherine Hamilton daubs rather than dabs at her eyes; Goethe herborises when he talks about plants.

Writing a novel is harder than Sontag realises. She said in an interview that she found it simpler than she expected, 'making things up'. It is easy for her, because she stays clear of the emotional discipline of the ideal novel-writer, the negative capability, the sway of empathy, the immediacy of realisation. The typical Sontag scene comes when Emma and Nelson kiss for the first time - a hard scene to make memorable, although it must carry some weight in the demands of the narrative. Sontag gets round the emotional demands by making it happen in a nobleman's folly where all the walls are broken mirrors 'as faceted as a fly's eye', so that the kiss 'was shattered, multiplied in the mirrors above', and we quickly lose interest in the people (if we ever had any) and are thrown back on contemplating their imaginary and symbolic images.

It is a clever way to make the moment stick, but it is not difficult to play out, once the idea has formed. Much harder would be to do the scene without the props, to get the weight of it just by the Emma-Horatio responses. But without such clever sets, without Sontag's critical games, and, let us not forget, without their historical reality, these characters would have little to hold us.

The sad thing is that if Sontag had pushed a bit harder in the other direction, she might have done something rather exciting. Where she lets herself rely on her own insights, we see that they have the irrational rightness and prescience of a natural novelist. So there are scenes to remember in the book: Marie Antoinette on the scaffold, feeling the yoke choking her; Emma Hamilton dancing the tarantella, 'orange with jaundice and bloated with fluids' or dying incognita in Paris, not even telling her daughter who she is, with the 'acrid stream of vomit' choking her last words.

That occasional sensual shock of recognition, if it had been extended, played on and trusted, would have made the novel truly forceful. The real problem is, Sontag does not trust fiction: 'Impossible to describe,' she makes Sir William reiterate on telling a tale. 'He can condescend, he can ironise. He can have an opinion . . . An odor. A taste. A touch. Impossible to describe.'

One day, with all her famed discipline and workaholism, Sontag may well produce a good novel; unfortunately this is not it. In the last analysis, it is not even particularly readable, the essay-snippets aside: there are too many lists, enumerations and abstractions in every chapter for the narrative to find its own rhythm. Although The Volcano Lover has gone to the bestseller lists in the States, I would guess that most of those buying it were accessorising rather than reading.

In this extract from The Volcano Lover, a statue comes to dinner:

A male statue who wakens - in the modern version, a machine given human form and then animated - comes to kill. And his being-really-a-statue packs him full with the martial virtue of single-mindedness, makes him unswervable, implacable, immune to the temptations of mercy.

It's a dinner party. Sophisticated people who have dressed up in handsome and revealing clothes are enjoying themselves in the atmosphere in which such dedicated partygoers enjoy themselves best - something of both brothel and salon, minus the exertions or risks of either. The food, whether chewy or delicate, is bountiful; the wine and champagne are costly; the lighting is muted and flattering; the music, and the aromas of flowers on the table, enveloping and suffusing; some sexual tomfoolery is taking place, both of the wanted and of the other kind ('We're just having fun,' says the would-be Don Juan, interfered with by the one who notices him relentlessly pressing his unwanted attentions on some woman); the servants are efficient and smile, hoping for a good tip. The chairs are yielding, and the guests profoundly enjoy the sensation of being seated. There are treats for all five senses. And mirth and glibness and flattery and genuine sexual interest. The music soothes and goads. For once, the gods of pleasure are getting their due.

And in comes this guest, this alien presence, who is not here to have fun at all. He comes to break up the party and haul the chief reveller down to hell. You saw him at the graveyard, atop a marble mausoleum. Being drunk with self-confidence, and also a little nervous about finding yourself in this cemetery, you made a joke to your sidekick. Then you halloed up to him. You invited him to the party. It was a morbid joke. And now he's here. He's grizzled, perhaps bearded, with a very deep voice and a lumbering, arthritic gait, not just because he is old but because he is made of stone; his joints don't bend when he walks. A huge, granite, forbidding father. He comes to execute judgment, a judgment you thought outmoded or that didn't apply to you. No, you cannot live for pleasure.

(Photograph omitted)