'When a huge police state devotes so much time, money and personnel to infiltrate the open society we have in the West, it gets results.'

'I don't like the Russians any more than you do,' said Trent. 'I was forced to work with them.'

'Because they threatened to report you to our security people. Yes, you told me all that.'

'You can sneer – you've no idea of what it's like.'

'But you knew how to handle it, didn't you? You did more and more spying. You grovelled before your pal Chlestakov and got him anything he wanted. For a man who doesn't like the Russians, you set an example of kindness and cooperation.'

'I knew that it wouldn't last for ever, that's why. I did many of the things they asked me but I took my time, and sometimes I said no. Sometimes I told Chlestakov that something wasn't possible. I played for time. I knew that eventually they would let me off the hook.'

'Why did you believe them? Why would any intelligence service let a well-placed agent off the hook?'

'Chlestakov guaranteed that, from the start.' Trent looked me in the eyes. 'And I believed him. It was just to be a temporary measure. He promised me that. I imposed other conditions too. He promised never to ask me about things that would endanger our own agents. He wanted general background information.'

'And a few little extra specifics,' I added.

'There were day-to-day things that Chlestakov needed for his official reports. He asked me about office routines and how the staff was rostered for duty. How old was Rensselaer, and did Cruyer own his house or have a mortgage? Many of his questions I couldn't answer, and some I didn't want to answer. But he told me that he had to have some such items that would impress Moscow.'

'He played on your sympathy, did he?' I asked sarcastically. 'If you didn't help poor old Chlestakov, he'd be moved to another assignment in some other town. And your sister wanted Chlestakov in London.'

'It may sound silly – '

'It sounds squalid,' I said. 'It sounds stupid and arrogant. Didn't you ever wonder if your treachery was worthwhile. Didn't you think your country was paying a high price for your sister's sex life?'

'Damn you.'

'Didn't you worry about being caught?'

'No.'

'Did Chlestakov not discuss with you the procedures he'd adopt if you came under suspicion? Didn't he tell you that he'd get you out of Britain if things went sour? Didn't he give you a number to phone if you had some security bloodhound asking you tricky questions?'

'I've told you all that before. We never talked about the possibility of my being caught.'

'And you've told me a pack of lies, Trent. Now I want some straight talking or you'll find yourself in another of our country houses, one where there won't be any walks in the garden or cigarettes with your lunch. Do I make myself clear?'

'You make yourself clear,' said Trent. My threats produced no real signs of fear in him – just suppressed anger. I could see a physical strength in him that matched his mental toughness. It was not the strength of the athlete but just the natural power of a man who'd grown up tall and strong. It was odd to think of Trent attempting suicide; still stranger to think of him failing to do it once his mind was made up, but I did not pursue the subject. We picked our way through the brambles and the bracken. There was the crack of twigs underfoot and the squelch of mud. Once a rabbit sprang out of the undergrowth and startled both of us.

It was Trent who spoke. 'I told them I could never go to Moscow. I'd sooner be in prison in England than go to Russia and die an exile. Chlestakov said that was all right. He said it would suit them. He said it was better that I'd told them that right from the start, because then he could make sure that I never got any information that could embarrass the KGB if said in court.'

'Embarrass the KGB! Is that the word he used? They put sane dissidents into lunatic asylums, consign thousands to their labour camps, they assassinate exiles and blackmail opponents. They must surely be the most ruthless, the most unscrupulous and the most powerful instrument of tyranny that the world has ever known. But dear old Chlestakov is frightened you might embarrass them.'

The past is past,' said Trent defensively. 'Tell me what you want of me now and I'll do it.'

'What does the postcard mean?'

'I'm to meet Chlestakov next Tuesday evening. I must phone Monday afternoon at three to be told the details.'

'I think it would be better if you cut through that one. Get hold of him and tell him it's an emergency. Tell him you were brought here and questioned after taking an overdose. Keep as near the true facts as you can.'

'Shall I say you questioned me?'

'Yes,' I said. 'Tell him you're frightened. Tell him the game's up. Tell him you're scared, really scared.'

Trent nodded.

'He'll ask you if anyone else has been questioned, and you'll say that everyone is being questioned. He'll ask you if we had any evidence, and you'll think about that and reluctantly admit that there was none.'

'None at all?'

'He'll tell you that it was the overdose that made us take you into custody, and you'll admit that that's probably true. I want it so that Chlestakov is reassuring you. So you keep whining. He'll ask you who is in charge of the investigation, and you'll give hum my name. He'll tell you that I'm not senior enough to make this a really important investigation. And he'll tell you that for something on the scale that you two are doing we'd bring investigators in from outside. Got all that?'

'You've made it quite clear.'

'And when the dust has settled on that exchange, you'll tell Chlestakov what a pity it is that you were silly enough to take that overdose, because you're now in a position to get something really big. Tell him you were going to write a report on the Berlin System – all the Berlin networks, every damn thing we are doing over there. That should make his mouth water.'

'I've never heard of the Berlin System.'

'He will have heard of it.'

'But now I won't be able to get it? Is that what I tell him?'

'Softly, softly. It will take time. You want to be quite sure you're no longer under any sort of suspicion. But this is really big stuff, tell him. This file contains all the facts and figures back for ten years and there will be all the CIA contacts and exchanges too.'

'And eventually you'll give me material to pass to him?' asked Trent. 'It's better if I know right at the start.'

'We won't let you down, Giles. We'll give you something that will make him happy and keep comrade Chlestakov where he can get his slippers warmed.'

'Keep my sister out of this.'

'Okay. I'll keep her out of it. But you'd better give me two hundred percent.'

'I will,' he said.

We came back through the shrubbery and onto the little humpbacked bridge. Trent stopped to light another cigarette, ducking into his coat collar to shelter the flame. I said, 'There's something I want to ask you. It's not important to the debriefing, I'm just curious.'

His head emerged in a cloud of blue smoke. He tossed the spent matchstick into the moat. Two ducks swam quickly towards it but, discovering it wasn't edible, moved away sedately. 'What then?' He was looking at the moat, with the dead leaves moving slowly on the current and the patches of weed swaying to the movement of the ducks.

'One night in September 1978 – '

'In 1978 I was in Berlin,' he said as if that would mean the end of the question.

'We all were,' I said. 'Fiona was there, Frank was there, I was there. Dicky was working in Frankfurt and he used to come to Berlin whenever he got the chance. Bret too. I want to ask you about a radio intercept that Signals got one night during the Baader-Meinhof panic. Remember?'