This was a new Werner Volkmann. This was not the introverted Jewish orphan I'd been at school with, nor the lugubrious teenager I'd grown up with in Berlin, nor the affluent, overweight banker who was welcome on both sides of the Wall. This new Werner was a tough, muscular figure in short-sleeved cotton shirt and well-fitting Madras trousers. His big droopy moustache had been trimmed and so had his bushy black hair. Being on holiday with his twenty-two-year-old wife had rejuvenated him.

He was standing on the sixth-floor balcony of a small block of luxury apartments in downtown Mexico City. From here was a view across this immense city, with the mountains a dark backdrop. The dying sun was turning the world pink, now that the stormclouds had passed over. Long ragged strips of orange and gold cloud were torn across the sky, like a poster advertising a smog-reddened sun ripped by a passing vandal.

The balcony was large enough to hold a lot of expensive white garden furniture as well as big pots of tropical flowers. Green leafy plants climbed overhead to provide shade, while a collection of cacti were arrayed on shelves like books. Werner poured a pink concoction from a glass jug. It was like a watery fruit salad, the sort of thing they pressed on you at parties where no one got drunk. It didn't look tempting, but I was hot and I took one gratefully.

Dicky Cruyer was flushed; his cowboy shirt bore dark patches of sweat. He had his blue-denim jacket slung over his shoulder. He tossed it on to a chair and reached out to take a drink from Werner.

Werner's wife Zena held out her glass for a refill. She was full-length on a reclining chair. She was wearing a sheer, rainbow-striped dress through which her suntanned limbs shone darkly. As she moved to sip her drink, German fashion magazines, balanced on her belly, slid to the ground and flapped open. Zena cursed softly. It was the strange, flat-accented speech of eastern lands that were no longer German. It was probably the only thing she'd inherited from her impoverished parents, and I had the feeling she would sometimes have been happier without it.

'What's in this drink?' I said.

Werner recovered the magazines from the floor and gave them to his wife. In business he could be tough, in friendships outspoken, but to Zena he was always indulgent.

Werner raised money from Western banks to pay exporters to East Germany, and then eventually collected the money from the East German government, taking a tiny percentage on every deal. 'Avalizing' it was called. But it wasn't a banker's business; it was a free-for-all in which many got their fingers burned. Werner had to be tough to survive.

'In the drink? Fruit juices,' said Werner. 'It's too early for alcohol in this sort of climate.'

'Not for me it isn't,' I said. Werner smiled but he didn't go anywhere to get me a proper drink. He was my oldest and closest friend; the sort of close friend who gives you the excoriating criticism that new enemies hesitate about. Zena didn't look up; she was still pretending to read her magazines.

Dicky had stepped into the jungle of flowers to get a clearer view of the city. I looked over his shoulder to see the traffic still moving sluggishly. In the street below there were flashing red lights and sirens as two police cars mounted the pavement to get around the traffic. In a city of fifteen million people there is said to be a crime committed every two minutes. The noise of the streets never ceased. As the flow of homegoing office workers ended, the influx of people to the Zona Rosa's restaurants and cinemas began. 'What a madhouse,' said Dicky.

A malevolent-looking black cat awoke and jumped softly down from its position on the footstool. It went over to Dicky and sank a claw into his leg and looked up at him to see how he'd take it. 'Hell!' shouted Dicky. 'Get away, you brute.' Dicky aimed a blow at the cat but missed. The cat moved very fast as if it had done the same thing before to other gringos.

Wincing with pain and rubbing his leg, Dicky moved well away from the cat and went to the other end of the balcony to look inside the large lounge with its locally made tiles, old masks and Mexican textiles. It looked like an arts and crafts shop, but obviously a lot of money had been spent getting it that way. 'Nice place you've got here,' said Dicky. There was more than a hint of sarcasm in his remark. It was not Dicky's style. Anything that departed much from Harrod's furniture department was too foreign for him.

'It belongs to Zena's uncle and aunt,' explained Werner. 'We're taking care of it while they're in Europe.' That explained the notebook I'd seen near the telephone. Zena had neatly entered 'wine glass', 'tumbler', 'wine glass', 'small china bowl with blue flowers'. It was a list of breakages, an example of Zena's sense of order and rectitude.

'You chose a bad time of year,' complained Dicky. 'Or rather Zena's uncle chose a good one.' He drained the glass, tipping it up until the ice cubes, cucumber and pieces of lemon slid down the glass and rested against his lips.

'Zena doesn't mind it,' said Werner, as if his own opinions were of no importance.

Zena, still concentrating on her magazine, said, 'I love the sun.' She said it twice and continued to read without losing her place.

'If only it would rain,' said Werner, 'It's this build-up to the storms that makes it so unbearable.'

'So you saw this chap Stinnes?' said Dicky very casually, as if that wasn't the reason that the two of us had dragged ourselves four thousand miles to talk to them.

'At the Kronprinz,' said Werner.

'What's the Kronprinz?' said Dicky. He put down his glass and used a paper napkin to dry his lips.

'A club.'

'What sort of club?' Dicky stuck his thumbs into the back of his leather belt and looked down at the toes of his cowboy boots reflectively. The cat had followed Dicky and looked as if it was about to reach up above his boot to put a claw into his thin calf again. Dicky aimed a vicious little kick at it but the cat was too quick for him. 'Get away,' said Dicky, more loudly this tune.

'I'm sorry about the cat,' said Werner. 'But I think Zena's aunt only let us use the place because we'd be company for Cherubino. It's your jeans. Cats like to claw at denim.'

'It bloody hurts,' said Dicky, rubbing his leg. 'You should get its claws clipped or something. In this part of the world cats carry all kinds of diseases.'

'What's it matter what sort of club?' said Zena suddenly. She closed the magazine and pushed her hair back. She looked different with her hair loose; no longer the tough little career girl, more the lady of leisure. Her hair was long and jet black and held with a silver Mexican comb which she brandished before tossing her hair back and fixing it again.

'A club for German businessmen. It's been going since 1902,' said Werner. 'Zena likes the buffet and dance they have on Friday nights. There's a big German colony here in the city. There always has been.'

'Werner said there would be a cash payment for finding Stinnes,' said Zena.

'There usually is,' said Dicky slyly, although he knew there would be no chance of a cash payment for such a routine report. It must have been Werner's way of encouraging Zena to cooperate with us. I looked at Werner and he looked back at me without changing his expression.

'How do you know it really is Stinnes?' said Dicky.

'It's Stinnes all right,' said Werner stoically. 'His name is on his membership card and his credit at the bar is in that name.'

'And his cheque book,' said Zena. 'His name is printed on his cheques.'

'What bank?' I asked.

'Bank of America,' said Zena. 'A branch in San Diego, California.'

'Names mean nothing,' said Dicky. 'How do you know this fellow is a KGB man? And, even if he is, what makes you so sure that this is the johnny who interrogated Bernard in East Berlin?' A brief movement of the hand in my direction. 'It might be someone using the same cover name. We've known KGB people do that. Right, Bernard?'