From his window he covered most of the approaches: eight or nine unequal roads and alleys which for no good reason had chosen Cambridge Circus as their meeting point. Between them, the buildings were gimcrack, cheaply fitted out with bits of empire: a Roman bank, a theatre like a vast desecrated mosque. Behind them, high- rise blocks advanced like an army of robots. Above, a pink sky was slowly filling with fog.

Why was it so quiet? he wondered. The theatre had long emptied but why didn't the pleasure trade of Soho, only a stone's- throw from his window, fill the place with taxis, groups of loiterers? Not a single fruit lorry had rumbled down Shaftesbury Avenue on its way to Covent Garden.

Through his binoculars Mendel once more studied the building straight across the road from him. It seemed to sleep even more soundly than its neighbours. The twin doors of the portico were closed and no light was visible in the ground-floor windows. Only on the fourth floor, out of the second window from the left, a pale glow issued and Mendel knew it was the duty officer's room; Smiley had told him. Briefly he raised the glasses to the roof, where a plantation of aerials made wild patterns against the sky; then down a floor to the four blackened windows of the radio section.

'At night everyone uses the front door,' Guillam had said. 'It's an economy measure to cut down on janitors.'

In those three hours, only three events had rewarded Mendel's vigil: one an hour is not much. At half past nine a blue Ford Transit delivered two men carrying what looked like an ammunition box. They unlocked the door for themselves and closed it as soon as they were inside, while Mendel murmured his commentary into the telephone. At ten o'clock the shuttle arrived: Guillam had warned him of this too. The shuttle collected hot documents from the out-stations and stored them for safekeeping at the Circus over the weekend. It called at Brixton, Acton and Sarratt in that order, said Guillam, lastly at the Admiralty, and it made the Circus by about ten. In the event it arrived on the dot of ten, and this time two men from inside the building came out to help unload; Mendel reported that too, and Smiley acknowledged with a patient 'Thank you'.

Was Smiley sitting down? Was he in the darkness like Mendel? Mendel had a notion he was. Of all the odd coves he had known, Smiley was the oddest. You thought, to look at him, that he couldn't cross the road alone, but you might as well have offered protection to a hedgehog. Funnies, Mendel mused. A lifetime of chasing villains and how do I end up? Breaking and entering, standing in the dark and spying on the Funnies. He'd never held with Funnies till he met Smiley. Thought they were an interfering lot of amateurs and college boys; thought they were unconstitutional; thought the best thing the Branch could do, for its own sake and the public's, was say 'Yes, sir, no, sir' and lose the correspondence. Come to think of it, with the notable exception of Smiley and Guillam, that's exactly what he thought tonight.

Shortly before eleven, just an hour ago, a cab arrived. A plain licensed London hackney cab, and it drew up at the theatre. Even that was something Smiley had warned him about: it was the habit within the service not to take taxis to the door. Some stopped at Foyles, some in Old Compton Street or at one of the shops; most people had a favourite cover destination and Alleline's was the theatre. Mendel had never seen Alleline but he had their description of him and as he watched him through the glasses he recognised him without a doubt, a big, lumbering fellow in a dark coat, even noticed how the cabby had pulled a bad face at his tip and called something after him as Alleline delved for his keys.

The front door is not secured, Guillam had explained, it is only locked. The security begins inside once you have turned left at the end of the corridor. Alleline lives on the fifth floor. You won't see his windows light up but there's a skylight and the glow should catch the chimney stack. Sure enough, as he watched, a patch of yellow appeared on the grimy brickwork of the chimney: Alleline had entered his room.

And young Guillam needs a holiday, thought Mendel. He'd seen that happen before, too: the tough ones who crack at forty. They lock it away, pretend it isn't there, lean on grown-ups who turn out not to be so grown up after all, then one day it's all over them, and their heroes come tumbling down and they're sitting at their desks with the tears pouring on to the blotter.

He had laid the receiver on the floor. Picking it up, he said: 'Looks like Tinker's clocked in.'

He gave the number of the cab, then went back to waiting. 'How did he look?' Smiley murmured.

'Busy,' said Mendel.

'So he should be.'

That one won't crack, though, Mendel decided with approval; one of your flabby oak trees, Smiley was. Think you could blow him over with one puff but when it comes to the storm he's the only one left standing at the end of it. At this point in his reflections a second cab drew up, squarely at the front entrance, and a tall slow figure cautiously climbed the steps one at a time like a man who takes care of his heart.

'Here's your Tailor,' Mendel murmured into the telephone. 'Hold on, here's Soldier- boy too. Proper gathering of the clans by the look of it. I say, take it easy.'

An old Mercedes 190 shot out of Earlham Street, swung directly beneath his window, and held the curve with difficulty as far as the northern outlet of the Charing Cross Road, where it parked. A young heavy fellow with ginger hair clambered out, slammed the door and clumped across the street to the entrance without taking the key out of the dash. A moment later another light went up on the fourth floor as Roy Bland joined the party.

All we need to know now is who comes out, thought Mendel.

Lock Gardens, which presumably drew its name from the Camden and Hampstead Road Locks nearby, was a terrace of four flat- fronted nineteenth-century houses built at the centre of a crescent, each with three floors and a basement and a strip of walled back garden running down to the Regent's Canal. The numbers ran two to five: number one had either fallen down or never been built. Number five made up the north end and as a safe house it could not have been improved, for there were three approaches in thirty yards and the canal towpath offered two more. To the north lay Camden High Street for joining traffic; south and west lay the parks and Primrose Hill. Better still, the neighbourhood possessed no social identity and demanded none. Some of the houses had been turned into one-roomed flats, and had ten door bells laid out like a typewriter. Some were got up grandly and had only one. Number five had two: one for Millie McCraig and one for her lodger Mr Jefferson.

Mrs McCraig was churchy and collected for everything, which was incidentally an excellent way of keeping an eye on the locals, though that was scarcely how they viewed her zeal. Jefferson, her lodger, was known vaguely to be foreign and in oil and away a lot. Lock Gardens was his pied- à-terre. The neighbours, when they bothered to notice him, found him shy and respectable. They would have formed the same impression of George Smiley if they happened to spot him in the dim light of the porch at nine that evening as Millie McCraig admitted him to her front room and drew the pious curtains.

She was a wiry Scottish widow with brown stockings and bobbed hair and the polished, wrinkled skin of an old man. In the interest of God and the Circus she had run Bible Schools in Mozambique and a seamen's mission in Hamburg and though she had been a professional eavesdropper for twenty years since then, she was still inclined to treat all menfolk as transgressors. Smiley had no way of telling what she thought. Her manner, from the moment he arrived, had a deep and lonely stillness; she showed him round the house like a chatelaine whose guests had long since died.

First the semi-basement where she lived herself, full of plants and that medley of old postcards, brass table tops and carved black furniture which seems to attach itself to travelled British ladies of a certain age and class. Yes, if the Circus wanted her at night they rang her on the basement phone. Yes, there was a separate line upstairs, but it was only for outgoing calls. The basement phone had an extension in the upstairs dining room. Then up to the ground floor, a veritable shrine to the costly bad taste of the housekeepers: loud Regency stripes, gilded reproduction chairs, plush sofas with roped corners. The kitchen was untouched and squalid. Beyond it lay a glass outhouse, half conservatory, half scullery, which looked down to the rough garden and the canal. Strewn over the tiled floor: an old mangle, a copper and crates of tonic water.

'Where are the mikes, Millie?' Smiley had returned to the drawing room. They were in pairs, Millie murmured, bedded behind the wallpaper, two pairs to each room on the ground floor, one to each room upstairs. Each pair was connected with a separate recorder. He followed her up the steep stairs. The top floor was unfurnished, save for an attic bedroom which contained a grey steel frame with eight tape machines, four up, four down.

'And Jefferson knows all about this?'

'Mr Jefferson,' said Millie primly, 'is run on a basis of trust.' That was the nearest she came to expressing her disapproval of Smiley, or her devotion to Christian ethics.

Downstairs again, she showed him the switches which controlled the system. An extra switch was fitted in each finger panel. Any time Jefferson or one of the boys, as she put it, wanted to go over to record, he had only to get up and turn down the left-hand light switch. From then on, the system was voice-activated; that is to say, the tape deck did not turn unless somebody was speaking.

'And where are you while all this goes on, Millie?'

She remained downstairs, she said, as if that were a woman's place.

Smiley was pulling open cupboards, lockers, walking from room to room. Then back to the scullery again, with its view to the canal. Taking out a pocket torch he signalled one flash into the darkness of the garden.

'What are the safety procedures?' Smiley asked, as he thoughtfully fingered the end light switch by the drawing-room door.

Her reply came in a liturgical monotone: 'Two full milk bottles on the doorstep, you may come in and all's well. No milk bottles and you're not to enter.'

From the direction of the sunroom came a faint tapping. Returning to the scullery Smiley opened the glazed door and after a hastily murmured conversation reappeared with Guillam.

'You know Peter, don't you, Millie?'

Millie might, she might not, her little hard eyes had fixed on him with scorn. He was studying the switch panel, feeling in his pocket as he did so.