'We'll walk to the end and see what else there is and then come back here and try some,' Dicky suggested. Dicky could always surprise me. Just as I had decided he was the archetypal gringo tourist, he wanted to have lunch at a fonda. 'So what's your theory?'

'I have no theory,' I said. 'Agents come in many shapes and sizes. Some are waiting for the socialist millennium, some hate their parents, some get angry after being ripped off by a loan company. Some simply want more money. But usually it begins with opportunity. A man finds himself handling something secret and valuable. He starts thinking about using that opportunity to get more money. Only then does he become a dedicated communist agent. So how does Biedermann fit into that? Where are his secrets? What's his motivation?'

'Guilt,' said Dicky. 'He feels guilty about his wealth.'

'If you'd ever met Paul Biedermann you'd know what a good joke that is.'

'Blackmail, then?'

'About what?'

'Sex.'

'Paul Biedermann would pay to have people say he was a sex maniac. He thinks of himself as a rich playboy.'

'You let your acute dislike of Paul Biedermann spill over into your judgements, Bernard. The fact of the matter is that Biedermann is an agent. You heard the two KGB people talking. He is an agent; it's no good your trying to convince yourself he's not.'

'Oh, he's an agent,' I said. 'But he's not the sort of agent that a man such as Stinnes would be running. That's what puzzles me.'

'Your experience makes you over-estimate what qualities an agent needs. Try and see it from their point of view: rich US businessman – someone the local cops would be reluctant to upset – isolated house on a lonely stretch of beach in western Mexico, not too far by road from the capital. And not too far by sea from Vladivostok.'

'Landing guns, you mean?'

'A man with a reputation for drinking who gets so rough with his servants that he's left all alone in the house. Wife and children often away. Convenient beach, pier big enough for a big motor boat.'

'Come along, Dicky,' I said. This is just a holiday cottage by Biedermann's standards. This is just a place he goes to read the Wall Street Journal and spend the weekend dreaming up a quick way to make a million or two.'

'So for half the year the house is completely empty. Then Stinnes and his pals have the place all to themselves. We know guns go from Cuba to Mexico's east coast and onwards by light plane. So why not bring them across the Pacific from the country where they are manufactured?' We'd got to the end of the food stalls and Dicky became interested in a stall selling pictures. There were family group photos and coloured litho portraits of generals and presidents. All of the pictures were in fine old frames.

'It doesn't smell right,' I said. But Dicky had put together a convincing scenario. If it was the house they were interested in, it didn't matter what kind of aptitude Biedermann had for being a field agent. Yes, London Central would love a report along those lines. It had the drama they liked. It had the geopolitic that called for maps and coloured diagrams. And, as a bottom line, it could be true.

'If it doesn't smell right,' said Dicky with heavy irony, 'I'll tell London to forget the whole thing.' He stood up straight as he looked at the selection of pictures for sale, and I realized he was studying his reflection in the glass-fronted pictures. He was too thin for a large, bright-green safari shirt. It made him look like a lollipop. 'Is it going to rain?' he said, looking at the time. He'd bought a new wrist-watch too. It was a multi-dial black chronometer that kept perfect time at 50 fathoms.

'It seldom rains in the morning, even during the rainy season.'

'It will bucket down on the stroke of noon, then,' said Dicky, looking up at the clouds that were now turning yellowish.

'I'm still not sure what London wants with Stinnes,' I said.

'London want Stinnes enrolled,' he said, as if he'd just remembered it. 'Shall we walk back to where the pork is? What did you say it's called – carnitas?'

'Enrolled?' It could mean a lot of things from persuaded to defect, to knocked on the head and rolled in a carpet. That would be difficult.'

The bigger they are the harder they fall,' said Dicky. 'You said yourself that he's forty years old and passed over for promotion. He's been stuck in East Berlin for ages. Berlin is a plum job for Western intelligence but it's the boondocks for their people. A smart KGB major left to rot in East Berlin is sure to be fretting.'

'I suppose his wife likes it there,' I said.

'What's that got to do with it?' said Dicky. 'Would I take an intelligence job in Canada because my wife liked ice hockey?'

'No, Dicky, you wouldn't.'

'And this fellow Stinnes will see what's good for him. Frank Harrington thought the chances were good.'

'You talked about all this with Frank?'

'Sure. Frank has to be in on it because Stinnes is based in Big B. Stinnes is very much in his territory, Bernard.' A nervous movement of fingers through curly hair. The worst difficulty is that the Data Centre showed that Stinnes has an eighteen-year-old son. That might prove sticky.'

'Christ, Dicky,' I said, as I came to terms with this bombshell. 'Did you know all this when we left London?'

'Enrolling Stinnes, you mean?'

'Yes, enrolling Stinnes I mean.'

'It looked as if it might go that way.' That was Dicky on the defensive. He'd known all along, that was obvious. I wondered what else he knew that he was not going to tell me about until it happened. 'London Central put out a departmental alert for him, didn't they?' We had reached the carnitas stand by now. He selected a chair that didn't wobble and sat down. 'I'll have mine wrapped in a tortilla; pork skin is very fattening.'

'London Central puts out departmental alerts for clerks who make off with the petty cash.'

'But they don't send senior staff, like us, to identify them when they are spotted,' said Dicky.

'Enrolled,' I said, considering all the implications. 'A hot-shot like Stinnes. You and me? It's madness.'

'Only if you start thinking it's madness,' said Dicky. 'My own opinion…' Pause. 'For what's it's worth…' A modest smile. '… is that we stand an excellent chance.'

'And when did you last enrol a KGB major?'

Dicky bit his lip. We both knew the answer to that one. Dicky was a pen-pusher. Stinnes was the first KGB officer Dicky had ever come this close to, and he hadn't seen Stinnes yet.

'Isn't London proposing to send someone over here to help? This is a complicated job, Dicky. We need someone who has experience.'

'Nonsense. We can do it. I don't want Bret Rensselaer breathing down my neck. If we can pull this one off, it will be a real coup.' He smiled. 'I didn't expect you to start asking London for help, Bernard. I thought you were the one who always liked to do everything on his own.'

'I'm not on my own,' I said. 'I'm with you.' The stallholder was stirring his cauldron of pork and arranging suitable pieces on a large metal platter.

'And you'd prefer to work with your friend Werner, eh?'

I could hear danger signals. 'We were at school together,' I said. 'I've known him a long time.'

'Werner Volkmann isn't even employed by the department. He hasn't been employed by us for years.'

'Officially that's right,' I said. 'But he's worked for us from time to time.'

'Because you give him jobs to do,' said Dicky. 'Don't try to make it sound as if the department employs him.'

'Werner knows Berlin,' I said.

'You know Berlin. Frank Harrington knows Berlin. Our friend Stinnes knows Berlin. There is no great shortage of people who know Berlin. That's no reason for employing Werner.'

'Werner is a Jew. He was born in Berlin when the Nazis were running things. Werner instinctively sees things in people that you and I have to learn about. You can't compare his knowledge of Berlin and Berliners with anything I know.'