'The Russians,' I said, having downed two generous glasses of Silas's magnificent wine as well as a few aperitifs, 'think you are all brutal Prussians.'

He nodded sadly. 'Yes, Saupreiss,' he said, using the Bavarian dialect word for Prussian swine. 'Perhaps you are right.'

After lunch the other guests divided into those who played billiards and those who preferred to sit huddled round the blazing log fire in the drawing room. My children were watching TV with Mrs Porter.

Silas, giving me a chance to speak privately with von Munte, took us to the conservatory to which, at this time of year, he had moved his house plants. It was a huge glass palace, resting against the side of the house, its framework gracefully curved, its floor formed of beautiful old decorative tiles. In these cold months the whole place was crammed full of prehensile-looking greenery of every shape and size. It seemed too cold in there for such plants to flourish, but Silas said they didn't need heat so much as light. 'With me,' I told him, 'it's exactly the opposite.'

He smiled as if he'd heard the joke before, which he had because I told it to him every time he trapped me into one of these chats amid his turnip tops. But Silas liked the conservatory, and if he liked it, everyone else had to like it too. He seemed not to feel the cold. He was jacketless, with bright red braces visible under his unbuttoned waistcoat. Walter von Munte was wearing a black suit of the, kind that was uniform for a German government official in the service of the Kaiser. His face was grey and lined and his whitening hair cropped short. He took off his gold-rimmed glasses and polished them on a silk handkerchief. Seated on the big wicker seat under the large and leafy plants the old man looked like some ancient studio portrait.

'Young Bernard has a question for you, Walter,' said Silas. He had a bottle of Madeira with him and three glasses. He put them on the table and poured a measure of the amber-coloured wine for each of us, then lowered his weight onto a cast-iron garden chair. He sat between us, positioned like a referee.

'It is not good for me,' said von Munte, but he took the glass and looked at the colour of it and sniffed it appreciatively.

'It's not good for anyone,' said Silas cheerfully, sipping his carefully measured portion. 'It's not supposed to be good for you. The doctor cut me down to one bottle per month last year.' He drank. 'This year he told me to cut it out altogether.'

'Then you are disobeying orders,' said von Munte.

'I got myself another doctor,' said Silas. 'We live in a capitalist society over here, Walter. I can afford to get myself a doctor who says it's okay to smoke and drink.' He laughed and sipped a little more of his, Madeira. 'Cossart 1926, bottled fifty years later. Not the finest Madeira I've ever encountered, but not at all bad, eh?' He didn't wait for our response, but selected a cigar from the box he'd brought under his arm. 'Try that,' he said, offering the cigar to me. 'That's an Upmann grand corona, one of the best cigars you can smoke and just right for this time of day. Walter, what about one of those petits that you enjoyed last night?'

'Alas,' said von Munte, holding up his hand to decline. 'I cannot afford your doctor. I must keep to one a week.'

I lit the cigar Silas had given me. It was typical of him that he had to select what he thought suitable for us. He had well-defined ideas about what everyone should have and what they shouldn't have. For anyone who called him a 'fascist' – and there were plenty who did -he had the perfect response: scars from Gestapo bullets.

'What do you want to ask me, Bernard?' said von Munte.

I got the cigar going and then I said, 'Ever hear of martello, harry, jake, see-saw or IRONFOOT?' I'd put in a few extra names as a means of control.

'What kind of names are these?' said von Munte. 'People?'

'Agents. Code names. Russian agents operating out of the United Kingdom.'

'Recently?'

'It looks as if one of them was used by my wife.'

'Yes, recently. I see.' Von Munte sipped his port. He was old-fashioned enough to be embarrassed at the mention of my wife and her spying. He shifted his weight on the wicker seat and the movement produced a loud creaking sound.

'Did you ever come across those names?' I asked.

'It was not the policy to let my people have access to such secrets as the code names of agents.'

'Not even source names?' I persisted. 'These are probably not agent names; they're the code names used in messages and for distribution. No real risk there, and the material from any one source keeps its name until identified and measured and pronounced upon. That's the KGB system and our system too.'

I glanced round at Silas. He was examining one of his plants, his head turned away as if he weren't listening. But he was listening all right; listening and remembering every last syllable of what was being said. I knew him of old.

'Source names. Yes, martello sounds familiar,' said von Munte. 'Perhaps the others too, I can't remember.'

'Two names used by one agent at the same time,' I said.

'That would be unprecedented,' said von Munte. He was loosening up now. 'Two names, no. How would we ever keep track of our material?'

'That's what I thought,' I said.

This was from the woman arrested in Berlin?' said Silas suddenly. He dropped the pretence of looking at his plants. 'I heard about that.' Silas always knew what was happening. In earlier days, while the D-G had been settling in, he'd even asked Silas to monitor some of the operations. Nowadays Silas and the D-G kept in touch. It would be foolish of me to imagine that this conversation would not get back to the Department.

'Yes, the woman in Berlin,' I said.

Walter von Munte touched his stiff white collar. 'I was never allowed to know any secrets. They gave me only what they thought I should have.'

I said, 'Like Silas distributing his food and cigars, you mean?' I kept wishing that Silas would depart and leave me and von Munte to have the conversation I wanted. But that was not Silas's way. Information was his stock in trade, it always had been, and he knew how to use it to his own advantage. That's why he'd survived so long in the Department.

'Not as generously as Silas,' said von Munte. He smiled and drank some of the Madeira and then shifted about, deciding how to explain it all. 'The bank's intelligence staff went over to the Warschauer Strasse office once a week. They would have all the new material in trays waiting for us. Old Mr Heine was in charge there. He'd produce for us each item according to subject.'

'Raw?' I said.

'Raw?' said von Munte. 'What does that mean?'

'Did they tell you what the agent said or did they merely tell you the content of his message?'

'Oh, the messages were edited, but otherwise as received. They had to be; the staff handling the material didn't know enough about economics to understand what it was about.'

'But you identified different sources?' I asked yet again.

'Sometimes we could, sometimes that was easy. Some of it was total rubbish.'

'From different agents?' I persisted. My God, but it was agony to deal with old people. Would I be like this one day?

'Some of their agents sent only rumours. There was one who never provided a word of good sense. They called him "Grock". That wasn't his code name or his source name; it was our joke. We called him "Grock", after the famous clown, of course.'

'Yes,' I said. But I'm glad von Munte had told me it was a joke; that gave me the cue to laugh. 'What about the good sources?' I said.

'You could recognize them from the quality of their intelligence and from the style in which it was presented.' He sat back in his chair. 'Perhaps I should explain what it was like in the Warschauer Strasse office. It wasn't our office. It is supposed to be an office belonging to Aeroflot, but there are always police and security guards on the door, and our passes were carefully scrutinized no matter how often we visited there. I don't know who else uses the building, but the economic intelligence staff met there regularly, as I said.'