'Are the people here all dealers?'

He looked round the sepulchral lounge. Waitresses in formal black dresses and white starched aprons padded silently to and fro across the white marble floor with trays of teas and cakes. The men, a mixed collection but for the most part middle-aged or elderly, were bent low, scribbling annotations in their catalogues and whispering conspiratorially to each other, rather as we were. 'I know most of them,' he said.

'And all men?'

'Yes, I don't know of one important female stamp dealer. There are virtually no female collectors even. Should a woman inherit a collection she sells almost immediately: you can depend upon it.' He decided his tea was cool enough to drink and tasted it.

I was flipping through the catalogue. 'How do they decide the estimated price?' I asked.

'Don't take much notice of that,' he said. 'That's just to whet your appetite. The estimated prices are far below what the auctioneer expects to get.'

'How much below?'

'There is no way to answer such a question. Auction houses vary. Crazy things happen. Sometimes two agents arrive, both instructed with buy bids.'

'What is a buy bid?'

'It means buy at any price.'

'At any price?'

'The craving – the reckless lust – that some collectors show for an item they particularly want is difficult to describe. Some collectors become unbalanced, there is no other word to describe it.' He fastidiously wiped his fingers on the napkin and then brought from his pocket a small folder of tough clear plastic. Inside it there was a used envelope (or what I'd learned to call a cover) with a stamp (or what I'd learned to call an adhesive) on it. 'Look at that.'

He handed me a white envelope adorned with quite an assortment of stamps and postmarks. Smudged and discoloured, it had been readdressed twice and was such a mess that I would probably have thrown it straight into the waste bin had I found it on my desk. It meant nothing to me but I looked at it with the kind of reverence he obviously expected of me. 'Most attractive,' I said.

'A man went to prison for that,' said Hoffmann. 'A respected man, chief clerk in an insurance office. He was a customer of mine: nearly fifty years old, with three children and a pensionable job. He had a decent little collection. I'd provided quite a lot of the things myself. He was knowledgeable about his own speciality. He regularly gave talks, and displayed his stamps to philatelic societies. Then he heard that a well-known collector had died and he knew that this cover was amongst the collection. It would be the gem that completed his collection. He asked me if I could find out when it was coming on the market. He was determined. By a lucky chance I knew about it. I guessed the widow would dispose of everything: they always do. You don't like to go sniffing round too soon. It upsets the family. On the other hand if you wait too long some other dealer will go in there and pick up the whole collection… buy it up for nothing sometimes, when the relatives don't know what they have inherited. There are some unscrupulous people in this business, I can tell you.'

'I'm beginning to believe it,' I said.

'Is there something wrong with your tea?'

'No. It's delicious.'

'You're not drinking it.'

'I'll get around to it.'

'The widow was a rich woman. The collection was unimportant to her. When I went there and asked her about the collection she decided to make me her agent, to value and then sell the whole lot of it. It put me in a difficult position in respect of the other collector but I never really considered that he was seriously in the market for it anyway. There are only thought to be four or five covers like that one. The last time one of them was auctioned it fetched fifty thousand dollars and that was almost ten years ago. Even if this one fetched no more than that one did, my insurance company friend just didn't have access to that sort of money.'

I looked at the cover. 'Fifty thousand dollars?' Could it be true?

Hoffmann nodded. No smile this time. They were serious people, these philatelists. 'In this year's catalogue the adhesives alone are listed at nearly that – of course catalogue values don't mean a lot – but I have a prospect in Munich… He's phoned me three times about it. He is becoming demented with the thought of owning it and insists that I let him see it… I am interested in hearing his assessment of its value. He spends a lot on his collection.'

'And your insurance friend?'

'The fool! He stole the money from his company. Filed a false claim, forged a cheque and made it payable to himself. Can you believe it? He was detected immediately. Pleaded guilty. His company said they had to prosecute him. There were too many other employees who might try the same trick. They were right of course, and he knows that. I went to see him yesterday.'

'In prison?' I handed the cover back to Hoffmann.

'Yes, in Graz. I gave evidence for him at the trial. I said he was honest and of good character but of course the evidence said he was a thief.'

'He must have been pleased to see you,' I said.

'I'm selling his collection too. He's flat broke now; the lawyers took his last penny. He's selling everything.' Hoffmann put the cover back into his pocket.

'Aren't you nervous about carrying a valuable thing like that?'

'Nervous? No.'

'What was the sentence?'

'My client?' He spoke through a mouthful of baba.

'The insurance man.'

He took his time in swallowing cake and then took some tea. 'Five years. I took him a colour photo of that cover.' He tapped his pocket. 'And the prison governor gave him special permission to have the picture in his cell.' Hoffmann sipped tea. 'The joke is that I'm beginning to think it's a forgery. In which case it's worthless.' He laughed down at his plate as if trying to resist it but finally ate the last of the cake.

'Did you know that right from the start?'

'Not for sure.' He wiped his lips.

'You suspected it?'

'I put it under the ultraviolet light. You can't be too careful. Then I took it to someone who knows. I'm still not certain one way or the other.' He drank more tea. 'Are you sure you wouldn't like a cream cake? They are delectable here, as light as a feather.'

'No thanks.'

'It's a weakness of mine,' he confessed. He'd finished the baba but left a huge blob of thick cream on the side of his plate. 'Not even apple strudel?'

'No.'

'You go into the auction and bid for Lot Number 584. It will come up in the morning at about ten o'clock but it would be safer if you were there a little early.' I looked at him. I recognized that this was my briefing: London Central had sent me here to buy. 'Pay cash for it. It is estimated at one thousand schillings. I will leave you three thousand Austrian schillings; that should be enough. Take it to Vienna and phone von Staiger. You've heard of the Baron, I suppose?'

'No,' I said.

He looked surprised. 'You won't actually meet him but there will be instructions for you.' He passed me a visiting card. Its printed content consisted only of Staiger's name and title and the description 'Investment Consultant'. In minuscule handwriting a Vienna address had been added in pencil. The use of aristocratic titles was illegal in Austria but Staiger, like many others, seemed not to care about that.

From his back pocket Hoffmann took his roll of money and counted out the Austrian notes. With it there was a small printed receipt form, of the sort sold in stationery shops. 'Sign there please,' he said.

I signed for the money. 'You won't be at the auction tomorrow?'

'Alas, no. I go to Munich tonight.' He smiled as he made sure my signature was legible and put the receipt away in his wallet. 'Hold up one of the number cards to bid. Sit at the front where the auctioneer can see you and then no one else in the room knows you are bidding. Your Lot will be ready for collection about five minutes after you've bought it. By paying cash you won't have to establish your credit or say who you are.'