'Who on earth are Clive's new Americans?' I murmured to Ned as we assembled like early worshippers round Brock's tape recorder in the situation room.

The London clock said six. Victoria Street had not yet begun its morning growl. The squeaking of the spool sounded like a chorus of starlings as Brock wound the tape in place. It had arrived by courier half an hour ago, having travelled overland by bag to Helsinki, then by special plane to Northolt. If Ned had been willing to listen to the technological tempters, we could have avoided the whole costly process, for the Langley wizards were swearing by a new device that transmitted spoken word securely. But Ned was Ned and he preferred his own tried methods.

He sat at his desk and was putting his signature to a document which he was shielding with his hand. He folded the paper, put it in its envelope and scaled the flap before handing it to tall Emma, one of his assistants. By then I had given up expecting a reply, so that his vehemence startled me.

'They're bloody carpetbaggers,' he snapped.

'From Langley?'

'God knows. Security.'

'Whose?' I insisted.

He shook his head, too furious to answer. Was it the document he had just signed that was annoying him, or the presence of the American interlopers? There were two of them. Johnny from their London station was escorting them. They wore navy blazers and short hair, and they had a Mormon cleanliness that I found slightly revolting. Clive stood between them, but Bob had sat himself demonstratively at the far end of the room with Walter, who looked wretched – I supposed at first because of the hour. Even Johnny seemed discomfited by their presence, and so immediately was I. These dull, unfamiliar faces had no place at the heart of our operation, and at such a crucial moment. They were like a gathering of mourners in advance of an anticipated death. But whose? I looked again at Walter and my anxieties were compounded.

I looked again at the new Americans, so slight, so trim, so characterless. Security, Ned had said. Yet why? And why now ? Why did they look at everyone except Walter? Why did Walter look at everyone except them? And why did Bob sit apart from them, and Johnny go on staring at his hands? I was grateful to have my thoughts interrupted.

We heard the boom of footsteps on wood stairs. Brock had started the recorder. We heard clunks and Barley's oath as he barked his back on the window frame. Then the shuffling of feet again as they clambered on to the rooftop.

It's a séance, I thought, as their first words reached us. Barley and Katya are addressing us from the great beyond. The immobile strangers with their executioners' faces were forgotten.

Ned was the only one of us with earphones. They made a difference, I later discovered when I tried them. You hear the Moscow doves shuffling on the gable and the rapid breathing inside Katya's voice. You hear the beating of your own joe's heart through the body mikes.

Brock played the whole rooftop scene before Ned ordered a break. Only our new Americans seemed unaffected. Their brown glances brushed each one of us but settled nowhere. Walter was blushing.

Brock played the dinner scene and still no one stirred: not a sigh or a creak or a hand clap, not even when he stopped the spool and wound it back.

Ned pulled off his earphones.

'Yakov Yefremovich, last name unknown, physicist, aged thirty in 1968, ergo born 1938,' he announced as he grabbed a pink trace request from the pile before him and scribbled on it. 'Walter, offers?'

Walter had to gather himself. He seemed distraught, and his voice had none of its usual flightiness. 'Yefrem, Soviet scientist, other names unknown, father of Yakov Yefremovich q.v., shot in Vorkuta after an uprising in the spring of '52,' he declared without looking at his pad. 'There can't be that many scientific Yefrems who were executed for an overdose of intelligence, even in dear Stalin's day,' he added rather pathetically.

It was absurd, but I fancied I saw tears in his eyes. Perhaps someone really has died, I thought, glancing once more at our two Mormons.

'Johnny?' said Ned, writing.

'Ned, we think we'll take Boris, other names unknown, widower, Professor of Humanities, Leningrad University, late 'sixties, one daughter Yekaterina,' said Johnny, still to his hands.

Ned seized another trace form, filled it in and tossed it into his out-tray like money he was pleased to throw away.

'Palfrey. Want to play?'

'Put me down for the Leningrad newspapers, will you please, Ned?' I said as airily as I could, given that Clive's Americans had turned their brown gaze full upon me. 'I'd like runners, starters and winners of the Mathematics Olympiad of 1952,' 1 said amid laughter. 'And for safety's sake perhaps you'd throw in '51 and '53 as well. And shall we add his academic medals, please, somewhere along the line? "He made candidate of sciences, he made doctor of sciences. He made everything, " she said. Can we have that, please? Thank you.'

When all the bids were in, Ned glared around for Emma to take the trace forms down to Registry. But that wasn't good enough for Walter who was suddenly determined to be counted - for, leaping to his feet, he marched fussily to Ned's desk, all five foot nothing of him, his little wrists flying out in front of him.

'I shall do all the ferreting myself,' he announced, in far too grand a tone, as he grabbed the pink bundle to his breast. 'This war is far too important to be left to our blue-rinse generals of Registry, irresistible though they may be.'

And I remember noticing how our Mormons watched him all the way to the door, then watched each other as we listened to his merry little heels prinking down the corridor. And I do not think I am speaking with hindsight when I tell you that my blood ran chill for Walter, without my having the smallest idea why.

'A breath of country air,' Ned told me onthe internal telephone an hour later when I was barely back at my desk at Head Office. 'Tell Clive I need you.'

'Then you'd better go, hadn't you?' said Clive, still closeted with his Mormons.

We had borrowed a fist Ford from the car pool. As Ned drove, he brushed aside my few attempts at conversation and handed me the file to read instead. We entered the Berkshire countryside but he still didn't talk. And when Brock rang on the car phone to give him some elliptical confirmation he required, he merely glunted, 'Then tell him,' and returned to his brooding.

We were forty miles from London, on the foulest planet of man's discovery. We were in the slums of modern science, where the grass is always nicely cut. The ancient gateposts were mastered by eroded sandstone lions. A polite in an in a brown sports jacket opened Ned's door. His colleague poked a detector underneath the chassis. Politely, they patted us both down.

'Taking the briefcase, are we, gentlemen?'

'Yes,' said Ned.

'Care to open it, sir?'

'No.'

'Dip it in the box, can we, gentlemen? We're not talking unexposed film, I presume, sir?'

'Please,' I said. 'Dip it in the box.'

We watched while they lowered the briefcase into what looked like a green coal bin, and took it out again.

'Thank you,' I said, taking it back.

'It's my pleasure, sir. Not at all, I'm sure.'

The blue van said FOLLOW ME. An Alsatian dog frowned at us from its barred rear window. The gates opened electronically and beyond them lay mounds of clipped grass like mass graves grown over. Olive downs stretched towards the sunset. A mushroom-shaped cloud would have looked entirely natural. We entered parkland. A pair of buzzards wheeled in the cloudless sky. High wire fenced off the hay fields. Smokeless brick buildings nestled in artful hollows. A noticeboard urged protective clothing in Zones D to K. A skull and crossbones said 'You Have Been Warned.' The van ahead of us was moving at a funeral's pace. We lumbered round a bend and saw empty tennis courts and aluminium towers. Lanes of coloured pipe jogged beside us, guiding us to a cluster of green sheds. At their centre, on a hilltop, stood the last vestige of the pre-nuclear age, a Berkshire cottage of brick and flint with 'Administrator' stencilled on the gate. A burly man came tripping down the crazy-paving path to greet us. He wore a blazer of British racing green and a tic with gold squash rackets on it, and a handkerchief shoved into his cuff

'You're from the Firm. Well done. I'm O'Mara. Which of you is who? I've told him to kick his heels in the lab till we whistle for him.'

'Good,' said Ned. O'Mara had grey-blond hair and an offhand regimental voice cracked by alcohol. His neck was puffy and his athlete's fingers were stained mahogany with nicotine. 'O'Mara keeps the long-haired scientists inline,' Ned had told me in one of our rare exchanges during the drive. 'He's half personnel, half security, all shit.'

The drawing-room had the air of being tended by Napoleonic prisoners of war. Even the bricks of the fireplace had been polished and the plaster lines between them picked out in loving white. We sat in rose-patterned armchairs drinking gin and tonic, lots of ice. Horse-brasses twinkled from the glistening black beams.

'Just come back from the States,' O'Mara recalled, as if accounting for our recent separation. He raised his glass and ducked his mouth to it, meeting it halfvay. 'You fellows go there a lot?'

'Occasionally,' said Ned.

'Now and then,' I said. 'When duty calls.'

'We send quite a few of our chaps out there on loan, actually. Oklahoma. Nevada. Utah. Most of them like it pretty well. A few get the heebie-jeebies, run for home.' He drank and took a moment to swallow. 'Visited their weapons laboratory at Livermore, out in California. Nice enough place. Decent guest house. Money galore. Asked us to attend a seminar on death. Bloody macabre if you think about it, but the shrinks seemed to believe it would do everybody good and the wines were extraordinary. I suppose if you're planning to consign large chunks of humanity to the flames you might as well know how it works.' He drank again, all the time in the world. The hilltop at that hour was a very quiet place. 'Surprising how many people hadn't given the subject much thought. Specially the young. The older ones were a bit more squeamish. They could remember the age of innocence, if it ever existed. You're aprompt fatality if you die straight off, and a soft one if you do it the slow way. I never realised. Gives a new meaning to the value of being at the centre of things, I suppose. Still, we're into the fourth generation now. Dulls the pangs. You chaps golfers?'

'No,' said Ned.