'They'd make an example of me. They'd cut my throat and make sure everyone knew why.'

'They'd not make an example of you,' I said. 'How could they? The last thing they want to do is draw attention to their secret financing network. No, as long as they thought you'd keep their secrets, they'd let you go, Paul. They'd huff and puff and shout and threaten in the hope you'd get frightened enough to keep going. But once they saw you were determined to end it they'd reconcile themselves to that.'

'If only I could believe it.' He blew a lot of smoke. 'One of the new clerks in my Mexico City office – a German fellow – has been asking me questions about some of the money I sent out. It's just a matter of time…'

'You don't let the staff in your office address the envelopes, do you?'

'No, of course not. But I do the envelopes on the addressing machine. I can't sit up all night writing out envelopes.'

'You're a fool, Paul.'

'I know,' he said sadly. 'This German kid was updating the address lists and he noticed these charities and trade unions that were all coded in the same way. It was in a different code from all the other addresses. I said it was part of my Christmas charity list but I'm not sure he believed me.'

'You'd better transfer him to one of your other offices,' I said.

'I'm going to send him to Caracas but it won't really solve the problem. Some other clerk will notice. I can't address the envelopes by hand and have handwritten evidence all over the place, can I?'

'Why are you telling me all this, Paul?'

'I've got to talk it over with someone.'

'Don't give me that,' I said.

He stubbed out his cigarette and said, 'I told the Russians that the British secret service was becoming suspicious. I invented stories about strangers making inquiries at various offices.'

'Did they believe that?'

'Phone calls. I always said the inquiries were phone calls. So I didn't have to describe anyone's physical appearance.' He went over to the side-table and picked up the bottle of brandy. He put it into a cupboard and shut the door. It looked like the simple action of a tidy man who didn't want to see bottles of booze standing around in his office.

'That was clever,' I said, although I thought such a device would sound very unconvincing to any experienced case officer.

'I knew they'd have to give me a respite if I was under surveillance.'

'And talking to me is a part of that scheme? Did you tell them about my phone call? Was it that that gave you the idea? Is that why they came here last night?'

He didn't answer my question, and that convinced me that my guess was right. Biedermann had thought up all this nonsense about the British becoming suspicious only after I'd phoned him. He said, 'You're something in the espionage business, you've admitted that. I realize you're not in any sort of senior position, but you must know people who are. And you're the only contact I have.'

I grunted. I didn't know whether that was Paul Biedermann's sincere opinion or whether he was hoping to provoke me into claiming power and influence.

'Does that mean you can help?' he said.

I finished the coffee and got to my feet. 'You copy that list of addresses for me – London might be interested in that – and I'll make sure that Bonn is told that we are investigating you. You'll become what NATO intelligence calls 'sacred'. None of the other security teams will investigate you without informing us. That will get back to your masters quickly enough.'

'Wait a moment, Bernd. I don't want Bonn restricting my movements or opening my mail.'

'You can't have it both ways, Paul. "Sacred" is the lowest category we have. There's not much chance that Bonn will find that interesting enough to do anything: they'll leave you to us.'

Biedermann didn't look too pleased at the idea of his reputation suffering, but he realized it was the best offer he was likely to get. 'Don't double-cross me,' he said.

'How would I do that?'

'I'm not up for sale to the highest bidder. I want out. I don't want to exchange a master in Moscow for a master in London.'

'You make me laugh, Paul,' I said. 'You really think you're a master spy, don't you? Are you sure you want to get out, or do you really want to get in deeper?'

'I need help, Bernd.'

'Where did you hide your car?'

'You can drive along the beach when the tide is out.'

I should have thought of that one. The tide comes in and washes away the tyre tracks. It had fooled Stinnes and his pal too. Sometimes amateurs can teach the pros a trick or two. 'The tide is out now,' I said. 'Get it and give me a lift into the village, will you, before someone starts renting my Chewy out as a bijou residence.'

'Keep the sweater,' he said. 'It looks good on you.'

'Muy complicado,' said Dicky. We were elbowing our way through a huge cobbled plaza that twice a week became one of Mexico City's busiest street markets, and he was listening to my account of the trip to Paul Biedermann's house. It was what Dicky called combining business with pleasure. 'Muy bloody complicado,' he said reflectively. That was Dicky's way of saying he didn't understand.

'Not very complicated,' I said. I'd found Biedermann's story depressingly simple – too simple, perhaps, to be the whole truth – but not complicated.

'Biedermann hiding in the bloody pool all night clasping a gun?' said Dicky with heavy irony. 'No, not complicated at all, of course.' He'd been chewing the nail of his little finger and now he inspected it. 'You're not telling me you believed all that stuff?'

The sun was very hot. Towering cumulus clouds were building up to the east and the humidity was becoming intolerable. We were walking down a line of vendors selling secondhand hardware that varied from ancient spark plugs to fake Nazi medals. Dicky stopped to look at some broken pottery figurines that a handwritten notice said were ancient Olmec. Dicky picked one up and looked at it. It looked too new to be genuine, but then so did many of the fragments in the National Museum.

Dicky passed it to me and walked on. I put it back on the ground with the other junk. I had too many broken fragments in my life already. I found Dicky looking at a basketful of silver-plated bracelets. 'I must get some little presents to take back to London,' he said.

'Which parts of Biedermann's story do you think were not true?' I asked him.

'Never mind the exam questions,' snapped Dicky. He didn't want to be in Mexico; he wanted to be in London making sure his job was secure. In some perverse way he blamed me for his situation, although, God knows, no one would have waved goodbye to him with more pleasure.

He began bargaining with the Indian squatting behind the folk-art jewellery. After a series of offers and counter-offers, Dicky agreed to buy six of them. He crouched down and solemnly began to sort through all of them to find the best six.

'I'm asking you what you believe and what you don't believe,' I said. 'Hell, Dicky. You're in charge. I need to know.'

Still crouched down, he looked at me from under the eyelashes that made him the heart-throb of the typing pool. He knew I was goading nun. 'You think I've been swanning around in Los Angeles wasting my time and the department's money, don't you?' Dicky was looking very Hollywood since his return from California. The faded jeans had gone, replaced by striped seersucker trousers and a short-sleeved green safari shirt with loops to hold rhino bullets.

'Why would I think that?'

Satisfied with his choice of bracelets, he sorted out his Mexican money and paid for them. He smiled and put the bracelets in the pocket of his shut. 'I saw Frank Harrington in LA. You didn't know I was going to see Frank, did you?'