Guillam gazed at him, waiting for the resolution. 'But what do you make of it?' he demanded, in a tone that suggested he had been cheated of the end. 'Did Karla ever really think of staying?'

'I'm sure it never crossed his mind,' said Smiley with disgust. 'I behaved like a soft fool. The very archetype of a flabby Western liberal. But I would rather be my kind of fool than his for all that. I am sure,' Smiley repeated vigorously, 'that neither my arguments nor his own predicament at Moscow Centre would ultimately have swayed him in the least. I expect he spent the night working out how he would outgun Rudnev when he got home. Rudnev was shot a month later, incidentally. Karla got Rudnev's job and set to work reactivating his old agents. Among them Gerald, no doubt. It's odd to reflect that all the time he was looking at me, he could have been thinking of Gerald. I expect they've had a good laugh about it since.' The episode had one other result, said Smiley. Since his San Francisco experience Karla had never once touched illegal radio. He cut it right out of his handwriting: 'Embassy links are a different matter. But in the field his agents aren't allowed to go near it. And he still has Ann's cigarette lighter.'

'Yours,' Guillam corrected him.

'Yes. Yes, mine. Of course. Tell me,' he continued, as the waiter took away his money, 'was Tarr referring to anyone in particular when he made that unpleasant reference to Ann?'

'I'm afraid he was. Yes.'

'The rumour is as precise as that?' Smiley enquired. 'And it goes that far down the line? Even to Tarr?'

'Yes.'

'And what does it say precisely?'

'That Bill Haydon was Ann Smiley's lover,' said Guillam, feeling that coldness coming over him which was his protection when he broke bad news, such as: you're blown; you're sacked; you're dying.

'Ah. I see. Yes. Thank you.'

There was a very awkward silence.

'And was there, is there a Mrs Gerstmann?' Guillam asked.

'Karla once made a marriage with a girl in Leningrad, a student. She killed herself when he was sent to Siberia.'

'So Karla is fireproof?' Guillam asked finally. 'He can't be bought and he can't be beaten?'

They returned to the car.

'I must say that was rather expensive for what we had,' Smiley confessed. 'Do you think the waiter robbed me?'

But Guillam was not disposed to chat about the cost of bad meals in England. Driving again, the day once more became a nightmare to him, a milling confusion of half-perceived dangers, and suspicions.

'So who's Source Merlin?' he demanded. 'Where could Alleline have had that information from, if not from the Russians themselves?'

'Oh, he had it from the Russians all right.'

'But for God's sake, if the Russians sent Tarr-'

'They didn't. Nor did Tarr use the British passports, did he? The Russians got it wrong. What Alleline had was the proof that Tarr had fooled them. That is the vital message we have learned from that whole storm in a teacup.'

'So what the hell did Percy mean about "muddying pools"? He must have been talking about Irina, for heaven's sake.'

'And Gerald,' Smiley agreed. Again they drove in silence, and the gap between them seemed suddenly unbridgeable.

'Look: I'm not quite there myself, Peter,' Smiley said quietly. 'But nearly I am. Karla's pulled the Circus inside out; that much I understand, so do you. But there's a last clever knot, and I can't undo it. Though I mean to. And if you want a sermon, Karla is not fireproof because he's a fanatic. And one day, if I have anything to do with it, that lack of moderation will be his downfall.'

It was raining as they reached Stratford tube station; a bunch of pedestrians was huddled under the canopy.

'Peter, I want you to take it easy from now on.'

'Three months without the option?'

'Rest on your oars a bit.'

Closing the passenger door after him, Guillam had a sudden urge to wish Smiley good night or even good luck, so he leaned across the seat and lowered the window and drew in his breath to call. But Smiley was gone. He had never known anyone who could disappear so quickly in a crowd.

Through the remainder of that same night, the light in the dormer window of Mr Barraclough's attic room at the Islay Hotel burned uninterrupted. Unchanged, unshaven, George Smiley remained bowed at the major's table, reading, comparing, annotating, cross-referring, all with an intensity which, had he been his own observer, would surely have recalled for him the last days of Control on the fifth floor at Cambridge Circus. Shaking the pieces, he consulted Guillam's leave rosters and sick lists going back over the last year and set these beside the overt travel pattern of Cultural Attaché Aleksey Aleksandrovich Polyakov, his trips to Moscow, his trips out of London as reported to the Foreign Office by Special Branch and the immigration authorities. He compared these again with the dates when Merlin apparently supplied his information and, without quite knowing why he was doing it, broke down the Witchcraft reports into those which were demonstrably topical at the time they were received, and those which could have been banked a month, two months before, either by Merlin or his controllers, in order to bridge empty periods: such as think pieces, character studies of prominent members of the administration, scraps of Kremlin tittle-tattle which could have been picked up any time and saved for a rainless day. Having listed the topical reports, he set down their dates in a single column and threw out the rest. At this point, his mood could best be compared with that of a scientist who senses by instinct that he is on the brink of a discovery and is awaiting any minute the logical connection. Later, in conversation with Mendel, he called it 'shoving everything into a test tube and seeing if it exploded'. What fascinated him most, he said, was the very point which Guillam had made regarding Alleline's grim warnings about muddied pools: he was looking, in other terms, for the 'last clever knot' which Karla had tied in order to explain away the precise suspicions to which Irina's letter had given shape.

He came up with some curious preliminary findings. First, that on the nine occasions when Merlin had produced a topical report, either Polyakov had been in London or Toby Esterhase had taken a quick trip abroad. Second, that over the crucial period following Tarr's adventure in Hong Kong this year, Polyakov was in Moscow for urgent cultural consultations; and that soon afterwards Merlin came through with some of his most spectacular and topical material on the 'ideological penetration' of the United States, including an appreciation of Centre's coverage of the major American intelligence targets.

Backtracking again, he established that the converse was also true: that the reports he had discarded on the grounds that they had no close attachment to recent events were those which most generally went into distribution while Polyakov was in Moscow or on leave.

And then he had it.

No explosive revelation, no flash of light, no cry of 'Eureka', phone calls to Guillam, Lacon, 'Smiley is a world champion'. Merely that here before him, in the records he had examined and the notes he had compiled, was the corroboration of a theory which Smiley and Guillam and Ricki Tarr had that day from their separate points of view seen demonstrated: that between the mole Gerald and the Source Merlin there was an interplay that could no longer be denied; that Merlin's proverbial versatility allowed him to function as Karla's instrument as well as Alleline's. Or should he rather say, Smiley reflected - tossing a towel over his shoulder and hopping blithely into the corridor for a celebratory bath - as Karla's agent? And that at the heart of this plot lay a device so simple that it left him genuinely elated by its symmetry. It had even a physical presence: here in London, a house, paid for by the Treasury, all sixty thousand pounds of it; and often coveted, no doubt, by the many luckless taxpayers who daily passed it by, confident they could never afford it and not knowing that they had already paid for it. It was with a lighter heart than he had known for many months that he took up the stolen file on Operation Testify.

To her credit, Matron had been worried about Roach all week, ever since she had spotted him alone in the washroom, ten minutes after the rest of his dormitory had gone down to breakfast, still in his pyjama trousers, hunched over a basin while he doggedly cleaned his teeth. When she questioned him, he avoided her eye. 'It's that wretched father of his,' she told Thursgood. 'He's getting him down again.' And by the Friday: 'You must write to the mother and tell her he's having a spell.'

But not even Matron, for all her motherly perception, would have hit on plain terror as the diagnosis.

Whatever could he do, he a child? That was his guilt. That was the thread that led directly back to the misfortune of his parents. That was the predicament that threw upon his hunched shoulders the responsibility night and day for preserving the world's peace. Roach the watcher - 'best watcher in the whole damn unit', to use Jim Prideaux's treasured words - had finally watched too well. He would have sacrificed everything he possessed, his money, his leather photograph case of his parents, whatever gave him value in the world, if it would buy him release from the knowledge which had consumed him since Sunday evening.

He had put out signals. On Sunday night, an hour after lights out, he had gone noisily to the lavatory, probed his throat, gagged and finally vomited. But the dormitory monitor, who was supposed to wake and raise the alarm - 'Matron, Roach's been sick' - slept stubbornly through the whole charade. Roach clambered miserably back into bed. From the callbox outside the staffroom next afternoon, he had dialled the menu for the day and whispered strangely into the mouthpiece, hoping to be overheard by a master, and taken for mad. No one paid him any attention. He had tried mixing up reality with dreams, in the hope that the event would be converted into something he had imagined; but each morning as he passed the Dip he saw again Jim's crooked figure stooping over the spade in the moonlight; he saw the black shadow of his face under the brim of his old hat, and heard the grunt of effort as he dug. Roach should never have been there. That also was his guilt: that the knowledge was acquired by sin. After a 'cello lesson on the far side of the village, he had returned to school with deliberate slowness in order to be too late for Evensong, and Mrs Thursgood's disapproving eye. The whole school was worshipping, all but himself and Jim: he heard them sing the Magnificat as he passed the church, taking the long route so that he could skirt the Dip, where Jim's light was glowing. Standing in his usual place, Roach watched Jim's shadow move slowly across the curtained window. He's turning in early, he decided with approval, as the light suddenly went out; for Jim had recently been too absent for his taste, driving off in the Alvis after rugger and not returning till Roach was asleep. Then the caravan door opened and closed and Jim was standing at the vegetable patch with a spade in his hand and Roach in great perplexity was wondering what on earth he should be wanting to dig for in the dark. Vegetables for his supper? For a moment Jim stood stock still, listening to the Magnificat, then glared slowly round and straight at Roach, though he was out of sight against the blackness of the hummocks. Roach even thought of calling to him; but felt too sinful on account of missing chapel.