It's like putting all your money on black, thought Guillam, staring out of the window of the café : everything you've got in the world, your wife, your unborn child. Then waiting, hour by hour, for the croupier to spin the wheel.

He had known Berlin when it was the world capital of the cold war, when every crossing point from East to West had the tenseness of a major surgical operation. He remembered how on nights like these, clusters of Berlin policemen and Allied soldiers used to gather under the arc lights, stamping their feet, cursing the cold, fidgeting their rifles from shoulder to shoulder, puffing clouds of frosted breath into each other's faces. He remembered how the tanks waited, growling to keep their engines warm, their gun barrels picking targets on the other side, feigning strength. He remembered the sudden wail of the alarm klaxons and the dash to the Bernauerstrasse or wherever the latest escape attempt might be. He remembered the fire brigade ladders going up; the orders to shoot back; the orders not to; the dead, some of them agents. But after tonight, he knew that he would remember it only like this : so dark you wanted to take a torch with you into the street, so still you could have heard the cocking of a rifle from across the river.

'What cover will he use?' he asked.

Smiley sat opposite him across the little plastic table, a cup of cold coffee at his elbow. He looked somehow very small inside his overcoat.

'Something humble,' Smiley said. 'Something that fits in. Those who cross here are mostly old-age pensioners, I gather.' He was smoking one of Guillam's cigarettes and it seemed to take all his attention.

'What on earth do pensioners want here?' Guillam asked.

'Some work. Some visit dependants. I didn't enquire very closely, I'm afraid.'

Guillam remained dissatisfied.

'We pensioners tend to keep ourselves to ourselves,' Smiley added, in a poor effort at humour.

'You're telling me,' said Guillam.

The café was in the Turkish quarter because the Turks are now the poor whites of West Berlin, and property is worst and cheapest near the Wall. Smiley and Guillam were the only foreigners. At a long table sat a whole Turkish family, chewing flat bread and drinking coffee and Coca-Cola. The children had shaven heads and the wide, puzzled eyes of refugees. Islamic music was playing from an old tape-recorder. Strips of coloured plastic hung from the hardboard arch of an Islamic doorway.

Guillam returned his gaze to the window, and the bridge. First came the piers of the overhead railway, next the old brick house that Sam Collins and his team had discreetly requisitioned as an observation centre. His men had been moving in surreptitiously these last two days. Then came the white halo of sodium arc lights, and behind it lay a barricade, a pillbox, then the bridge. The bridge was for pedestrians only, and the only way over it was a corridor of steel fencing like a bird walk, sometimes one man's width and sometimes three. Occasionally one crossed, keeping a meek appearance and a steady pace in order not to alarm the sentry tower, then stepping into the sodium halo as he reached the West. By daylight the bird walk was grey; by night for some reason yellow, and strangely bright. The pillbox was a yard or two inside the border, its roof just mastering the barricade, but it was the tower that dominated everything, one iron-black rectangular pillar at the bridge's centre. Even the snow avoided it. There was snow on the concrete teeth that blocked the bridge to traffic, snow swarmed round the halo and the pillbox and made a show of settling on the wet cobble; but the sentry tower was immune, as if not even the snow would go near it of its own free will. Just short of the halo, the bird walk narrowed to a last gateway and a cattle pen. But the gateway, said Toby, could be closed electrically at a moment's notice from inside the pillbox.

The time was ten-thirty but it could have been three in the morning, because along its borders, West Berlin goes to bed with the dark. Inland, the island-city may chat and drink and whore and spend its money; the Sony signs and rebuilt churches and conference halls may glitter like a fair-ground; but the dark shores of the borderland are silent from-seven in the evening. Close to the halo stood a Christmas tree, but only the upper half of it was lit, only the upper half was visible from across the river. It is a place of no compromise, thought Guillam, a place of no third way. Whatever reservations he might occasionally have about the Western freedom, here, at this border, like most other things, they stopped dead.

'George?' said Guillam softly, and cast Smiley a questioning glance.

A labourer had lurched into the halo. He seemed to rise into it as they all did the moment they stepped out of the bird walk, as if a burden had fallen from their backs. He was carrying a small brief-case and what looked like a railman's lamp. He was slight of build. But Smiley, if he had noticed the man at all, had already returned to the collar of his brown overcoat and his lonely, far-away thoughts. 'If he comes, he'll come on time,' Smiley had said. Then why do we get here two hours early? Guillam had wanted to ask. Why do we sit here, like two strangers, drinking sweet coffee out of little cups, soaked in the steam of this wretched Turkish kitchen, talking platitudes? But he knew the answer already. Because we owe , Smiley would have said if he had been in a talking mood. Because we owe the caring and the waiting, we owe this vigil over one man's effort to escape the system he has helped create. For as long as he is trying to reach us, we are his friends. Nobody else is on his side.

He'll come, Guillam thought. He won't. He may. If this isn't prayer, he thought, what is it?

'More coffee, George?'

'No, thank you, Peter. No, I don't think so. No.'

'They seem to have soup of some sort. Unless that was the coffee.'

'Thank you. I think I've consumed about all I can manage,' said Smiley, in quite a general tone, as if anyone who wished to hear was welcome.

'Well, maybe I'll just order something for rent,' said Guillam.

'Rent? I'm sorry. Of course. God knows what they must live on.'

Guillam ordered two more coffees and paid for them. He was paying as he went, deliberately, in case they had to leave in a hurry.

Come for George's sake, he thought; come for mine. Come for all our damn sakes, and be the impossible harvest we have dreamed of for so long.

'When did you say the baby was due, Peter?'

'March.'

'Ah. March. What will you call it?'

'We haven't really thought.'

Across the road, by the glow of a furniture shop that sold reproduction wrought iron and brocade and fake muskets and pewter, Guillam made out the muffled figure of Toby Esterhase in his Balkan fur hat, affecting to study the wares. Toby and his team had the street, Sam Collins had the observation pose that was the deal. For the escape cars, Toby had insisted on taxis, and there they stood, three of them, suitably shabby, in the darkness of the station arches, with notices in their windscreens saying 'OUT OF SERVICE', and their drivers standing at the Imbiss- stand, eating sausages in sweet sauce out of paper dishes.

The place is a total minefield, Peter , Toby had warned. Turks, Greeks, Yugoslavs, a lot of crooks - even the damn cats are wired, no exaggeration.

Not a whisper anywhere , Smiley had ordered. Not a murmur, Peter. Tell Collins.

Come, thought Guillam urgently. We're all rooting for you. Come.

From Toby's back, Guillam lifted his gaze slowly to the topfloor window of the old house where Collins' observation post was sited. Guillam had done his Berlin stint, he had been part of it a dozen times. The telescopes and cameras, the directional microphones, all the useless hardware that was supposed to make the waiting easier; the crackle of the radios, the stink of coffee and tobacco; the bunk-beds. He imagined the co-opted West German policeman who had no idea why he had been brought here, and would have to stay till the operation was abandoned or successful - the man who knew the bridge by heart and could tell the regulars from the casuals and spot the smallest bad omen the moment it occurred : the silent doubling of the watch, the Vopo sharpshooters easing softly into place.

And if they shoot him? thought Guillam. If they arrest him? If they leave him - which they would surely like to, and had done before to others - bleeding to death, face downward in the bird walk not six feet from the halo?

Come , he thought, less certainly, willing his prayers into the black skyline of the East. Come all the same.

A fine, very bright pin-light flitted across the west-facing upper window of the observation house, bringing Guillam to his feet. He turned round to see Smiley already half-way to the door. Toby Esterhase was waiting for them on the pavement.

'It's only a possibility, George,' he said softly, in the tone of a man preparing them for disappointment. 'Just a thin chance, but he could be our man.'

They followed him without another word. The cold was ferocious. They passed a tailor's shop with two dark-haired girls stitching in the window. They passed wall posters offering cheap ski holidays, death to Fascists, and to the Shah. The cold made them breathless. Turning his face from the swirling snow, Guillam glimpsed a children's adventure playground made of old railway sleepers. They passed between black, dead buildings, then right, across the cobbled road, in pitch-frozen darkness to the river bank, where an old timber bullet-shelter with rifle slits offered them the whole span of the bridge. To their left, black against the hostile river, a tall wooden cross, garnished with barbed wire, bore memory to an unknown man who had not quite escaped.

Toby silently extracted a pair of field-glasses from his overcoat and handed them to Smiley.

'George. Listen. Good luck, okay?'

Toby's hand closed briefly over Guillam's arm. Then he darted away again, into the darkness.

The shelter stank of leaf-mould and damp. Smiley crouched to the rifle slit, the skirts of his tweed coat trailing in the mud, while he surveyed the scene before him as if it held the very reaches of his own long life. The river was broad and slow, misted with cold. Arc lights played over it, and the snow danced in their beams. The bridge spanned it on fat stone piers, six or eight of them, which swelled into crude shoes as they reached the water. The spaces between them were arched, all but the centre, which was squared off to make room for shipping, but the only ship was a grey patrol boat moored at the Eastern bank, and the only commerce that it offered was death. Behind the bridge, like its vastly bigger shadow, ran the railway viaduct, but like the river it was derelict, and no trains ever crossed. The warehouses of the far bank stood monstrous as the hulks of an earlier barbaric civilization, and the bridge with its yellow bird walk seemed to leap from half-way up them, like a fantastic light-path out of darkness. From his vantage point, Smiley could scan the whole length of it with his field-glasses, from the floodlit white barrack house on the Eastern bank, up to the black sentry tower at the crest, then slightly downhill again towards the Western side : to the cattle pen, the pillbox that controlled the gateway, and finally the halo.