'We put to Merlin your follow-up question about the prevailing Kremlin view on the sale of Russian oil surpluses to the United States. We suggested to him, at your request, that this was at odds with his report last month that the Kremlin is presently flirting with the Tanaka government for a contract to sell Siberian oil on the Japanese market. Merlin saw no contradiction in the two reports and declined to forecast which market might ultimately be favoured.'

Whitehall regretted its temerity.

'Merlin will not repeat not add to his report on the repression of Georgian nationalism and the rioting in Tbilisi. Not being himself a Georgian, he takes the traditional Russian view that all Georgians are thieves and vagabonds, and better behind bars...'

Whitehall agreed not to press.

Merlin had suddenly drawn nearer. Was it only the acquisition of a London house which gave Smiley this new sense of Merlin's physical proximity? From the remote stillness of a Moscow winter, Merlin seemed suddenly to be sitting here before him in the tattered room; in the street outside his window, waiting in the rain, where now and then, he knew, Mendel kept his solitary guard. Here out of the blue was a Merlin who talked and answered back and gratuitously offered his opinions: a Merlin who had time to be met. Met here in London? Fed, entertained, debriefed in a sixty-thousand-pound house while he threw his weight about and made jokes about Georgians? What was this circle of knowledge which had now formed itself even within the wider circle of those initiated into the secrets of the Witchcraft operation?

At this point, an improbable figure flitted across the stage: one JPR, a new recruit to Whitehall's growing band of Witchcraft evaluators. Consulting the indoctrination list, Smiley established that his full name was Ribble, and that he was a member of Foreign Office Research Department. J. P. Ribble was puzzled.

JPR to the Adriatic Working Party (AWP): 'May I respectfully draw your attention to an apparent discrepancy concerning dates? Witchcraft No. 104 (Soviet-French discussions on joint aircraft production) is dated April 21st. According to your covering minute, Merlin had this information directly from General Markov on the day after the negotiating parties agreed to a secret exchange of notes. But on that day, April 21st, according to our Paris Embassy, Markov was still in Paris and Merlin, as witness your report No. 109, was himself visiting a missile research establishment outside Leningrad...'

The minute cited no fewer than four similar 'discrepancies', which put together suggested a degree of mobility in Merlin that would have done credit to his miraculous namesake.

J. P. Ribble was told in as many words to mind his own business. But in a separate minute to the Minister, Alleline made an extraordinary admission which shed an entirely new light on the nature of the Witchcraft operation.

'Extremely secret and personal. We spoke. Merlin, as you have known for some time, is not one source but several. While we have done our best for security reasons to disguise this fact from your readers, the sheer volume of material makes it increasingly difficult to continue with this fiction. Might it not be time to come clean, at least on a limited basis? By the same token it would do the Treasury no harm to learn that Merlin's ten thousand Swiss francs a month in salary, and a similar figure for expenses and running costs, are scarcely excessive when the cloth has to be cut so many ways.'

But the minute ended on a harsher note: 'Nevertheless, even if we agree to open the door this far, I regard it as paramount that knowledge of the existence of the London house, and the purpose for which it is used, remain absolutely at a minimum. Indeed, once Merlin's plurality is published among our readers, the delicacy of the London operation is increased.'

Totally mystified, Smiley read this correspondence several times. Then, as if struck by a sudden thought, he looked up, his face a picture of confusion. So far away were his thoughts, indeed, so intense and complex, that the telephone rang several times inside the room before he responded to the summons. Lifting the receiver, he glanced at his watch; it was six in the evening, he had been reading barely an hour.

'Mr Barraclough? This is Lofthouse from finance, sir.'

Peter Guillam, using the emergency procedure, was asking by means of the agreed phrases for a crash meeting and he sounded shaken.

The Circus archives were not accessible from the main entrance. They rambled through a warren of dingy rooms and half landings at the back of the building, more like one of the secondhand bookshops which proliferate round there, than the organised memory of a large department. They were reached by a dull doorway in the Charing Cross Road jammed between a picture-framer and an all-day café that was out of bounds to staff. A plate on the door read 'Town and Country Language School, Staff Only' and another 'C and L Distribution Ltd'. To enter you pressed one or other bell and waited for Alwyn, an effeminate Marine who spoke only of weekends. Till Wednesday or so he spoke of the weekend past, after that he spoke of the weekend to come. This morning, a Tuesday, he was in a mood of indignant unrest.

'Here, what about that storm then?' he demanded as he pushed the book across the counter for Guillam to sign. 'Might as well live in a lighthouse. All Saturday, all Sunday. I said to my friend: "Here we are in the middle of London and listen to it." Want me to look after that for you?'

'You should have been where I was,' said Guillam, consigning the brown canvas grip into Alwyn's waiting hands. 'Talk about listen to it, you could hardly stand upright.'

Don't be over-friendly, he thought, talking to himself.

'Still I do like the country,' Alwyn confided, stowing the grip in one of the open lockers behind the counter. 'Want a number then? I'm supposed to give you one, the Dolphin would kill me if she knew.'

'I'll trust you,' said Guillam. Climbing the four steps he pushed open the swing doors to the reading room. The place was like a makeshift lecture hall: a dozen desks all facing the same way, a raised area where the archivist sat. Guillam took a desk near the back. It was still early - ten ten by his watch - and the only other reader was Ben Thruxton of research, who spent most of his time here. Long ago, masquerading as a Latvian dissident, Ben had run with revolutionaries through the streets of Moscow calling death to the oppressors. Now he crouched over his papers like an old priest, white-haired and perfectly still.

Seeing Guillam standing at her desk, the archivist smiled. Quite often, when Brixton was dead, Guillam would spend a day here searching through old cases for one that could stand retiring. She was Sal, a plump, sporting girl who ran a youth club in Chiswick and was a judo black belt.

'Break any good necks this weekend?' he asked, helping himself to a bunch of green requisition slips.

Sal handed him the notes she kept for him in her steel cupboard.

'Couple. How about you?'

'Visiting aunts in Shropshire, thank you.'

'Some aunts,' said Sal.

Still at her desk he filled in slips for the next two references on his list. He watched her stamp them, tear off the flimsies, and post them through a slot on her desk.

'D corridor,' she murmured, handing back the top copies. 'The two-eights are halfway on your right, the three-ones are next alcove down.'

Pushing open the far door, he entered the main hall. At the centre an old lift like a miner's cage carried files into the body of the Circus. Two bleary juniors were feeding it, a third stood by to operate the winch. Guillam moved slowly along the shelves reading the fluorescent number cards.

'Lacon swears he holds no file on Testify at all,' Smiley had explained in his usual worried way. 'He has a few resettlement papers on Prideaux and nothing else.' And in the same lugubrious tone: 'So I'm afraid we'll have to find a way of getting hold of whatever there is in Circus Registry.'

For 'getting hold', in Smiley's dictionary, read 'steal'. One girl stood on a ladder. Oscar Allitson the collator was filling a laundry basket with wrangler files, Astrid the maintenance man was mending a radiator. The shelves were wooden, deep as bunks and divided into pigeon-holes by panels of ply. He already knew that the Testify reference was four-four eight-two E, which meant alcove forty-four, where he now stood. E stood for extinct and was used for dead operations only. Guillam counted to the eighth pigeon-hole from the left. Testify should be second from the left but there was no way of making certain because the spines were unmarked. His reconnaissance complete, he drew the two files he had requested, leaving the green slips in the steel brackets provided for them.

'There won't be much, I'm sure,' Smiley had said, as if thinner files were easier. 'But there ought to be something, if only for appearances.' That was another thing about him that Guillam didn't like just then: he spoke as if you followed his reasoning, as if you were inside his mind all the time.

Sitting down he pretended to read but passed the time thinking of Camilla. What was he supposed to make of her? Early this morning as she lay in his arms she told him she had once been married. Sometimes she spoke like that: as if she'd lived about twenty lives. It was a mistake, so they packed it in.

'What went wrong?'

'Nothing. We weren't right for each other.'

Guillam didn't believe her.

'Did you get a divorce?'

'I expect so.'

'Don't be damn silly, you must know whether you're divorced or not!'

His parents handled it, she said; he was foreign. 'Does he send you money?'

'Why should he? He doesn't owe me anything.'

Then the flute again, in the spare room, long questioning notes in the half light while Guillam made coffee. Is she a fake or an angel? He'd half a mind to pass her name across the records. She had a lesson with Sand in an hour.

Armed with a green slip with a four-three reference, he returned the two files to their places and positioned himself at the alcove next to Testify.

'Dry run uneventful,' he thought.

The girl was still up her ladder. Allitson had vanished but the laundry basket was still there. The radiator had already exhausted Astrid and he was sitting beside it reading the Sun. The green slip read four-three four-three and he found the file at once because he had already marked it down. It had a pink jacket like Testify. Like Testify it was reasonably thumbed. He fitted the green slip into the bracket. He moved back across the aisle, again checked Allitson and the girls, then reached for the Testify file and replaced it very fast with the file he had in his hand.