Bret, not knowing exactly what was coming, and never ready to state his views without time to think, made a sound that indicated measured agreement.

'But I have seen a lot of them,' said Silas, 'and I know something of what makes such fellows tick. Fiona Samson will not wind down slowly like a neglected clock. She'll keep going at full power until she has nothing more to give. Then, like a light bulb, she'll glow extra bright before going out.'

It sounded too melodramatic to Bret. He looked at Silas wondering if this same little speech, with other names, had been used many times before, like next-of-kin letters when the unthinkable happened. He couldn't decide. He nodded. 'When the question of her going over there was first discussed, I was in favour of taking the husband into our confidence.'

'I know you were. But his ignorance has proved a great asset to us, and to his wife. It's given her a good start. Now it's up to her.' Silas looked around him in a proprietorial manner and crushed a clod of earth with the toe of his heavy boot. It was good fertile soil, dark and rich with leafmould.

Bret undid his borrowed windcheater and fingered a bundle of computer printout to be sure he hadn't dropped it during his walk.

It was hot in the garden, everything silent and still, protected by the high garden walls. This was the culmination of the gardener's year. There was billowing greenery everywhere but all too soon the summer would be over; the leaves withered; the earth cold and hard. 'Look at these maincrop carrots,' said Silas. He bent over to grab the feathery leaves. For a moment he seemed on the point of uprooting one but then he changed his mind and let go. 'Carrots are tricky,' said Silas. 'They grow to maturity and you have to decide whether to lift them and store them or leave them in the earth.'

Bret nodded.

'Leave them in the earth and you get a sweeter-tasting carrot but if there is a really severe frost, you lose them.' He found a carrot and pulled it up. It was small and thin but of a beautiful colour. 'On the other hand if you lift them, you can be sure that they haven't been got at by the worms and slugs. See what I mean, Bret?'

'So how do you decide when to pull them?'

'I consult,' said Silas. 'I talk to the experts.'

Bret decided to ignore the wider implications of Silas's agricultural nostrums and return to the subject of Bernard Samson. 'But once that decision was taken, it might have been wiser to move Bernard Samson out of Operations. He's too damned curious about what exactly happened.'

'That's natural enough,' said Silas.

'He pries and asks questions. On that account, and a few others too, Samson was not the man to send to talk to a potential KGB defector in Mexico City, or anywhere else.'

'Why?' asked Silas sardonically. 'Because he hasn't been to University?'

'This KGB fellow: Stinnes – whatever his motives or intentions – will be expecting an Oxbridge man. Sending a blue-collar type like Samson will make him think he doesn't rate.'

'You're a dedicated Anglophile, Bret. No disrespect, I'm delighted that you should be. But it sometimes leads you into an exaggerated regard for our old British institutions.'

Bret stiffened. 'I have always supported Samson, even when he was at his most intractable. But Oxford and Cambridge attract the most competitive students, and will always be the Department's finest source of recruits. I'd hate to see the day come when that policy changed.'

Silas ran his hand lovingly over the outdoor tomatoes. One of them, full size and deep red, he picked and weighed in his hand. 'Oxford and Cambridge provide an excellent opportunity to learn, although not better than any well-motivated student can find in a first-class library. But an Oxbridge education can make graduates feel that they are members of some privileged elite, destined to lead and make decisions that will be inflicted upon lesser beings. Such elitism must of necessity be based upon expectations that are often unfulfilled. Thus Oxbridge has not only provided Britain with its most notable politicians and civil servants but its most embittered traitors too.' Silas smiled sadly, as if the traitors had played a long-forgiven and half-forgotten prank upon him.

'Elite?' said Bret. 'You'd search a long way to find someone more arrogant than Bernard Samson.'

'Bernard's arrogance comes from something inside him: some vitality, force and a seemingly inexhaustible fund of courage. Our great universities will never be able to furnish inner strength, no one can. What teachers provide is always superimposed upon the person that already exists. Education is a carapace, a cloak laid upon the soul: a protection, a coloration or something to hide inside.'

To get the conversation back on to a more practical plane Bret said, 'And Samson drinks too much.'

'That's rather judgemental,' said Silas. 'Few of us would be absolved from that one, truth be told.' Silas took a clasp-knife and cut the tomato in hah to study it before biting a piece out of it.

'You're right, of course,' said Bret deferentially, and added, 'Remember I recommended Samson for the German Desk.'

Silas swallowed the piece of tomato but some of the juice dribbled down his chin. He wiped his mouth with the back of his hand and said, 'Indeed you did. But you didn't do it with enough vigour and follow-through to get it for him.'

'I plead the Fifth, Silas.' Bret decided not to explain that his decision was deliberate and reasoned: it would take too long. 'But let's not argue. Samson and Cruyer are both in Mexico. We have a lot riding on this one; a careless move now could set us back severely.'

'Yes, we must move with great caution,' said Silas. 'We have the woman installed in the East and now we must hope that all continues to go well for her. No contact yet?' He offered the remaining half of tomato to Bret, but Bret shook his head. Silas threw the tomato on to the rubbish.

'No, Silas, no contact. I'm leaving her alone for as long as possible. It's not primarily an intelligence-gathering operation at this stage of the game. I think you and the D-G both agreed that it shouldn't be. We said that right at the start.'

'Yes, Bret, we did. She has enough problems, I'm sure.'

'For the time being, let her masters digest the material she's providing them with.' Bret had been moving restlessly, looking round to be sure that they were not observed or overheard. Now he fixed his eyes on Silas. 'But before too long we must provide the Soviets with some really solid affirmation of Mrs Samson's creed. It's going well but we must exploit and reinforce success.' These final words were spoken with fervour.

Silas looked blankly at Bret. The words Bret had emphasized were the sort of axiom to be found in the works of Sun-tzu, Vegetius, Napoleon or some wretch of that ilk. Silas did not believe that such teachings embodied truths of any relevance to the craft of espionage, but decided that this was not the right time to take that up with Bret.

Thinking that Silas might not have heard, Bret said it again. 'We must exploit and reinforce success.'

Silas looked at him and nodded. Despite that glacial personality there was a certain boyish enthusiasm in Bret, a quality not unusual in Americans of any class. Bret combined it with another American characteristic: the self-righteous passion of the crusader. Silas had always thought of him as warrior prince: hand-woven silk under the heavy armour, marching through the desert behind the True Cross. Austere and calculating, Bret would have made an invincible Richard the Lionheart but an equally convincing Saladin.

Silas said, 'I hope you're not thinking of anything costly, Bret. The other evening I calculated that the code and cipher changes and so on that the D-G ordered after Mrs Samson went over there must have cost the Department nearly a million sterling. Add in the costs that we don't shoulder, I'd say there was a worldwide bill for three million. And that's without the incalculable loss efface we suffered at losing her.'