'The airliner hijack – I remember that clearly enough. Frank Harrington seemed to think it had all been done to discredit him.' Trent smiled. It was as near as he came to making a joke.

'There was a special inquiry about this Russian Army signal.'

Trent turned to look at me. 'Yes, I remember that. Frank let an American do the questioning. It was a fiasco.'

'A fiasco?'

Trent shrugged but said nothing.

'You went into the main building,' I said, 'and into Operations at the end of your duty shift. You saw the signal… maybe on Fiona's desk.'

'The night of the big panic? Who said I was in Operations?'

'Fiona. You went up to collect her and take her home.'

'Not that night, I didn't.'

'Are you sure? You're not telling me you weren't permitted in Operations?'

'Well, officially I wasn't, but anyone who wore a badge could get into the main building. I'm not denying I gate-crashed Operations regularly. But I didn't do it when I knew Frank was up there holding court and laying down the law. Hell, you know what Frank is like. I've seen him blast a senior man because he'd moved a fire extinguisher out of his office.'

'Frank's a bit obsessed about fire precautions,' I said. 'We all know that.'

'Well, he's obsessed about a few other things, including people from the annex going into Operations without an Ops pass. No, I didn't go up there that night. The word went round that Frank was throwing a fit because Bonn thought the mayor of Berlin was going to be kidnapped, and we all stayed well away from him.'

'It was just a signal intercept from Karlshorst…'

He nodded. 'News of which got back to Karlshorst within three days, and they changed codes and wavelengths. Yes, I know all about it. That American fellow… Joe something – "Just call me Joe," he kept saying – '

'Joe Brody.'

'Joe Brody. He explained the whole thing.'

'Let's make it off the record,' I said.

'Off the record, on the record – it makes no difference. I didn't go up there that night.'

'Fiona told me you did,'

'Then Fiona is not telling you the truth.'

'Why should she lie about it?' I said.

'That's something you'll have to ask Fiona.'

'Did you get the information by some other means? I'm determined to press this point, Giles. You may as well come clean.'

'Because your pal Werner Volkmann did it? And you'd like to clear him?'

'How did Werner get into Operations that night? He's never worked in Operations. He's always been a street man.'

'Werner Volkmann wasn't up there. He was Signals Security One. He brought it from Signals to Ciphers that night.'

'That's all? But Werner would have to be some wizard to decipher a message while he's travelling five blocks in the back of a car.'

Trent smoked reflectively. 'The theory was that Werner Volkmann was hanging around the cipher room that night. He could have seen the deciphered message. Anyway, he didn't have to decipher it in order to tell the Russians that their traffic was being intercepted. He only had to recognize the heading or the footing codes and the time and the Karlshorst Army transmitter identification. The Russians would know exactly what had been intercepted without Werner ever knowing what the message was.'

'Do you believe it was Werner?'

'Brody is a very careful investigator. He gave everyone a chance to speak their piece. Even Fiona was interrogated. She handled the message. I never saw the report, of course, but it concluded that Volkmann was the most likely person of those who could have done it.'

'I said, did you believe Volkmann did it.'

'No,' said Trent. 'Werner's too lazy to be a double agent – too lazy to be a single agent, from what I saw of him.'

'So who could have done it?'

'Frank hates Werner, you know. He'd been looking for a chance to get rid of him for ages.'

'But someone still has to have done it. Unless you think Frank leaked his own intercept just as a way of putting the blame on Werner.'

'It's possible.'

'You can't be serious.'

'Why not?'

I said, 'Because if Frank wants to get rid of Werner, he's only got to fire him. He doesn't have to go to all the trouble of leaking an intercept to the Russians.'

'It wasn't a vitally important piece of intelligence,' said Trent. 'We've seen more important things than that used as Spielzeug just to boost the reputation of a double agent.'

'If Frank wanted to fire him, he could have fired him,' I repeated.

'But what if Frank wanted him discredited?'

I stared at Trent and thought about it. 'I suppose you're right,' I said.

'Werner Volkmann spread stories about Frank.'

'Stories?'

'You've heard Werner when he's had a few beers. Werner is always able to see scandal where none exists. He had stories about Frank fiddling money from the non-accountable funds. And stories about Frank chasing the typists around the filing cabinets. I suppose Frank got fed up with it. You keep telling stories like that and finally people are going to start believing them. Right?'

'I suppose so,' I said.

'Someone leaked it,' said Trent. 'If it wasn't Volkmann or Frank, then Moscow had someone inside Operations that night. And it certainly wasn't me.'

'God knows,' I said, as if I'd lost interest in the mystery. But now I was sure that the Karlshorst intercept was vitally important, because it was the only real slip Moscow 's well-placed man had made.

'What do you think will happen?' said Trent. What was going to happen to him, he meant.

'You've had a long time in this business,' I reminded him. 'Longer than I have. You know how these things work. Do you know how many people just as guilty as you are have retired from the service with an unconditional pardon and a full pension?'

'How many?' said Trent. He knew I couldn't answer and that amused him.

'Plenty,' I said. 'People from Five, people from Six, a couple of Special Branch people, and those three from Cheltenham that you helped to interrogate last year.'

Trent said nothing. We watched four men as they came out of the house and went down the gravel path towards the gate lodge. One of them skipped half a pace in order to keep step with the others. They were security guards, of course. Only such men are that anxious to keep in step with their fellows. 'I hate prisons,' he said. He said it conversationally, as a man might remark upon his dislike of dinner parties or sailing.

'You've never been inside, have you?'

'No.'

'It's not like this, believe me. But let's hope it won't come to that – not for you, not for anyone.'

'That's called "leaving the door open",' said Trent. It was a subheading in his training report.

'Don't dismiss it on that account,' I said. But we both knew that Trent had written: 'Promise the interviewee anything. Promise him freedom. Promise him the moon. He'll be in no position to argue with you afterwards.'