The philosophy was simple. The task of an intelligence service, Smiley announced firmly, was not to play chase games but to deliver intelligence to its customers. If it failed to do this, those customers would resort to other, less scrupulous sellers or, worse, indulge in amateurish self-help. And the service itself would wither. Not to be seen in the Whitehall markets was not to be desired, he went on. Worse: unless the Circus produced, it would also have no wares to barter with the Cousins, nor with other sister services with whom reciprocal deals were traditional. Not to produce was not to trade, and not to trade was to die.

Amen, they said.

His theory - he called it his premise - on how intelligence could be produced with no resources, was the subject of an informal meeting held in the rumpus room not two months after his accession, between himself and the tiny inner circle which made up, to a point, his team of confidants. They were in all five: Smiley himself; Peter Guillam, his cupbearer; big, flowing Connie Sachs, the Moscow-gazer; Fawn, the dark-eyed factotum, who wore black gym-shoes and manned the Russian-style copper samovar and gave out biscuits; and lastly Doc di Salis, known as the Mad Jesuit, the Circus's head China watcher. When God had finished making Connie Sachs, said the wags, He needed a rest, so He ran up Doc de Salis from the remnants. The Doc was a patchy, grubby little creature, more like Connie's monkey than her counterpart, and his features, it was true, from the spiky silver hair that strayed over his grimy collar, to the moist misshapen fingertips which picked like chicken beaks at everything around them, had an unquestionably ill-begotten look. If Beardsley had drawn him, he would have had him chained and hirsute, peeping round the corner of her enormous caftan. Yet di Salis was a notable orientalist, a scholar, and something of a hero too, for he had spent a part of the war in China, recruiting for God and the Circus, and another part in Changi jail, for the pleasure of the Japanese. That was the team: the Group of Five. In time it expanded, but to start with these five alone made up the famous cadre, and afterwards, to have been one of them, said di Salis, was 'like holding a Communist Party card with a single-figure membership number'.

First, Smiley reviewed the wreck, and that took some while, in the way that sacking a city takes some while, or liquidating great numbers of people. He simply drove through every back alley the Circus possessed, demonstrating quite ruthlessly how, by what method, and often exactly when Haydon had laid bare its secrets to his Soviet masters. He had of course the advantage of his own interrogation of Haydon, and of the original researches which had led him to Haydon's discovery. He knew the track. Nevertheless, his peroration was a minor tour de force of destructive analysis.

'So no illusions,' he ended tersely. 'This service will never be the same again. It may be better, but it will be different.'

Amen again, they said, and took a doleful break to stretch their legs.

It was odd, Guillam recalled later, how the important scenes of those early months seemed all to play at night. The rumpus room was long and raftered, with high dormer windows which gave on to nothing but orange night sky and a coppice of rusted radio aerials, war relics which no one had seen fit to remove.

The premise, said Smiley when they had resettled, was that Haydon had done nothing against the Circus that was not directed, and that the direction came from one man personally: Karla.

His premise was, that in briefing Haydon, Karla was exposing the gaps in Moscow Centre's knowledge; that in ordering Haydon to suppress certain intelligence which came the Circus's way, in ordering him to downgrade or distort it, to deride it, or even to deny it circulation altogether, Karla was indicating the secrets he did not want revealed.

'So we can take the backbearings, can't we, darling?' murmured Connie Sachs, whose speed of uptake put her as usual a good length ahead of the rest of the field.

'That's right, Con. That's exactly what we can do,' said Smiley gravely. 'We can take the backbearings.' He resumed his lecture, leaving Guillam for one more mystified than before.

By minutely charting Haydon's path of destruction - his pugmarks as he called them - by exhaustively recording his selection of files; by reassembling, after aching weeks of research if necessary, the intelligence culled in good faith by Circus outstations, and balancing it, in every detail, against the intelligence distributed by Haydon to the Circus's customers in the Whitehall market place, it would be possible to take backbearings - as Connie so rightly called them - and establish Haydon's, and therefore Karla's, point of departure, said Smiley.

Once a correct backbearing had been taken, surprising doors of opportunity would open, and the Circus, against all outward likelihood, would be in a position to go over to the initiative - or, as Smiley put it - 'to act, and not merely to react.'

The premise, to use Connie Sachs's joyous description later, meant: 'Looking for another bloody Tutankhamun, with George Smiley holding the light and us poor Charlies doing the digging.'

At that time, of course, Jerry Westerby was not even a twinkle in their operational eye.

They went into battle next day, huge Connie to one corner, the crabbed little di Salis to his. As di Salis said, in a nasal, deprecating tone, which had a savage force: ' At least we do finally know why we're here.' Their families of pasty burrowers carved the archive in two. To Connie and 'my Bolshies' as she called them, went Russia and the Satellites. To di Salis and his 'yellow perils', China and the Third World. What fell between -source reports on the nation's theoretical Allies, for instance - was consigned to a special wait-bin for later evaluation. They worked, like Smiley himself, impossible hours. The canteen complained, the janitors threatened to walk out, but gradually the sheer energy of the burrowers infected even the ancillary staff and they shut up. A bantering rivalry developed. Under Connie's influence, backroom boys and girls who till now had scarcely been seen to smile, learned suddenly to chaff each other in the language of their great familiars in the world outside the Circus. Czarist imperialist running dogs drank tasteless coffee with divisive, deviationist chauvinist Stalinists and were proud of it. But the most impressive blossoming was unquestionably in di Salis, who interrupted his nocturnal labours with short but vigorous spells at the ping-pong table, where he would challenge all comers, leaping about like a lepidopterist after rare specimens. Soon the first fruits appeared, and gave them fresh impetus. Within a month, three reports had been nervously distributed, under extreme limitation, and even found favour with the sceptical Cousins. A month later a hardbound summary wordily entitled Interim report on lacunae in Soviet intelligence regarding Nato sea to air strike capacity, earned grudging applause from Martello's parent factory in Langley, Virginia, and an exuberant phone call from Martello himself.

'George, I told those guys!' he yelled, so loud that the telephone line seemed an unnecessary extravagance, 'I told them: The Circus will deliver. Did they believe me. Did they hell!'

Meanwhile, sometimes with Guillam for company, sometimes with silent Fawn to babysit, Smiley himself conducted his own dark peregrinations and marched till he was half dead with tiredness. And still without reward, kept marching. By day, and often by night as well, he trailed the home counties and points beyond, questioning past officers of the Circus and former agents out to grass. In Chiswick, perched meekly in the office of a cut-price travel agent and talking in murmurs to a former Polish colonel of cavalry resettled as a clerk there; he thought he had glimpsed it; but like a mirage, the promise dissolved as he advanced on it. In a secondhand radio shop in Sevenoaks a Sudeten Czech held out the same hope to him, but when he and Guillam hurried back to confirm the story from Circus records, they found the actors dead and no one left to lead him further. At a private stud in Newmarket, to Fawn's near-violent fury, he suffered insult at the hand of a tweedy and opinionated Scot, a protégé of Smiley's predecessor Alleline, all in the same elusive cause. Back home, he called for the papers, only once more to see the light go out.

For this was the last and unspoken conviction of the premise which Smiley had outlined in the rumpus room: that the snare with which Haydon had trapped himself was not unique. That in the end-analysis, it was not Haydon's paperwork which had caused his downfall, not his meddling with reports, nor his 'losing' of inconvenient records. It was Haydon's panic. It was Haydon's spontaneous intervention in a field operation, where the threat to himself, or perhaps to another Karla agent, was suddenly so grave that his one hope was to suppress it despite the risk. This was the trick which Smiley longed to find repeated. And this was the question which, never directly, but by inference, Smiley and his helpers in the Bloomsbury reception centre canvassed:

'Can you remember any incident during your service in the field when in your opinion you were unreasonably restrained from following an operational lead?'

And it was dapper Sam Collins, in his dinner jacket,: with his brown cigarette and his trim moustache and his Mississippi dandy's smile, summoned for a quiet chat one day, who breezed in to say: 'Come to think of it, yes, old boy, I can.'

But behind this question again, and Sam's crucial answer, stalked the formidable person of Miss Connie Sachs and her pursuit for Russian gold.

And behind Connie again, as ever, the permanently misted photograph of Karla.

'Connie's got one, Peter,' she whispered to Guillam over the internal telephone late one night. 'She's got one, sure as boots.'

It was not her first find by any means, not her tenth, but her devious instinct told her straight away it was 'the genuine article, darling, mark old Connie's words'. So Guillam told Smiley and Smiley locked up his files and cleared his desk and said: ' All right, let her in.'

Connie was a huge, crippled, cunning woman, a don's daughter, a don's sister, herself some sort of academic, and known to the older hands as Mother Russia. The folklore said Control had recruited her over a rubber of bridge while she was still a debutante, on the night Neville Chamberlain promised 'peace in our time'. When Haydon came to power in the slipstream of his protector Alleline, one of his first and most prudent moves was to have Connie put out to grass. For Connie knew more about the byways of Moscow Centre than most of the wretched brutes, as she called them, who toiled there, and Karla's private army of moles and recruiters had always been her very special joy. Not a Soviet defector, in the old days, but his debriefing report had passed through Mother Russia's arthritic fingers; not a coat-trailer who had manoeuvred himself alongside an identified Karla talent-spotter, but Connie greedily rehearsed him in every detail of the quarry's choreography; not a scrap of hearsay over nearly forty years on the beat which had not been assumed into her pain-racked body, and lodged there among the junk of her compendious memory, to be turned up the moment she rummaged for it. Connie's mind, said Control once, in a kind of despair, was like the back of one enormous envelope. Dismissed, she went back to Oxford and the devil. At the time Smiley reclaimed her, her only recreation was The Times crossword and she was running at a comfortable two bottles a day. But that night, that modestly historic night, as she hauled her great frame along the fifth floor corridor toward George Smiley's inner room, she sported a clean grey caftan, she had daubed a pair of rosy lips not far from her own, and she had taken nothing stronger than a vile peppermint cordial all day long - of which the reek lingered in her wake -and a sense of occasion, they all decided afterwards, was stamped on her from the first. She carried a heavy plastic shopping bag, for she would countenance no leather. In her lair on a lower floor, her mongrel dog, christened Trot, and recruited on a wave of remorse for its late predecessor, whimpered disconsolately from beneath her desk, to the lively fury of her roommate di Salis, who would often privately lash at the beast with his foot; or in more jovial moments content himself with reciting to Connie the many tasty ways in which the Chinese prepared their dogs for the pot. Outside the Edwardian dormers, as she passed them one by one, a racing late-summer rain was falling, ending a long drought, and she saw it - she told them all later - as symbolic, if not Biblical. The drops rattled like pellets on the slate roof, flattening the dead leaves which had settled there. In the anteroom the mothers continued stonily with their business, accustomed to Connie's pilgrimages, and not liking them the better for it.