Elsa refused to accompany us. To be in my flat opened up for her a present and future for which as abbess she must have longed, and she was bubbling with mischief and gaiety.

‘I’d be a distraction,’ she insisted. ‘You know what they’d be curious about instead of attending to the bowl. What a pretty piece! You should ask her out to lunch, Tony. Who does she belong to, Colet or Matravers-Drummond? And what would they think of you if it came out that you’d raped me?’

There was, of course, only one answer to that piece of impertinence.

I set out next morning with the cauldron in a case used for packing top hats and a feeling that I might be walking into trouble. The police had been informed that among objects stolen from Broom Lodge was a gold bowl. The description of it had been very imprecise, but jewellers and bullion brokers might have been advised to look out for something of the sort. It seemed possible, though very unlikely, that the British Museum had also been warned. I was happier when I called for the major at his club. He had bought a new shirt and tie and looked a personage above suspicion who might easily be lord-lieutenant of his county but could never have been a burglar, even amateur.

We took a taxi to the Musum and were ushered in to the curator’s office. I was impressed by Sir Anthony, who struck me as an authority on art rather than archaeology, which may have been due to his neat, pointed, seventeenth-century beard and the jeweller’s loup slung from a broad black ribbon round his neck. So much the better. The bowl had authorities of two different disciplines to pronounce on it.

Up to a point I came clean. I said that Major Matravers-Drummond in the course of his investigations into esoteric religions had become involved with a strange character who claimed to have rediscovered the secrets of alchemy and had shown him the golden bowl as proof. The major pretended to believe that he had made it and managed to obtain the loan of it for a day. He had appealed to me for an opinion as I was the only expert at hand, not realising that I was a historian of ancient economies and certainly no archaeologist.

Polite chorus of: ‘No, no. You are well known, Colet. Admirable work in your own field.’

Well, I had ruled out transmutation of metals, I said, and when I had seen the bowl or cauldron I thought it more likely that the self-styled alchemist was trying to fake an antiquity. I had also wondered whether it might not be a genuine treasure from some undeclared discovery of a chieftain’s hoard or tomb.

I then took the lid off the hat box and placed my beauty upon the table. They were both fascinated by it, but the curator ruled out my buried hoard immediately.

‘The gold is thin and unless very solidly protected from falling material it would have been squashed flat or at least dented by earth or pebbles. But there is only one small dent below the rim which looks recent. My dear Piers, it resembles nothing I have ever seen – Scythian, Scandinavian, Persian, Egyptian. I don’t care for the handles, and my personal opinion is that two years old is more likely than two thousand.’

Sir Anthony praised to the skies the craftsman who had made it, but added that as an antiquity it would not take in a … he was about to say ‘child’ but substituted ‘competent archaeologist’.

‘We must ask ourselves first what it was for. A cooking pot? Well, you wouldn’t dare put it on a hot fire. A mixing vessel? But that would be a bowl without neck or rim. A burial urn? Wrong shape. The vessel depends for its astonishing beauty on its form. No decoration at all, which is exceptional. A bed-ridden emperor’s urinal. That’s the best I can suggest. And what’s your opinion, Denzil? You sit there saying nothing and looking guilty. How about that second sight of yours?’

‘I can only tell you that in some way it is not of our world at all,’ the major said.

‘Made at the full moon by a cabalist, eh? But there is something odd about the glorious colour…’ he fixed the loup in his eye and carried the cauldron to the window. ‘I have my suspicions. May I send it down to the lab, Denzil? You can trust them, they won’t need filings. And meanwhile shall we have a small decanter of the Museum manzanilla?’

The verdict did not take long to come back – the time for two leisurely glasses of sherry and some learned conversation on the techniques of Cretan and Mycenaean goldsmiths to which I contributed little and the major nothing – beyond saying that his alchemist friend was a recluse, worked to his own taste and didn’t know whom he was imitating if he was.

The bowl was brought back and a note handed to Sir Anthony.

‘As I suspected might be the case,’ he pronounced, ‘your cauldron or amphora is of pure gold. 24 carats. Pure. No ancient craftsman would ever have worked in pure gold without any alloy. It’s too malleable for any practical purpose. With strong arms you could squash this vessel fairly flat between your palms. Off-hand I can think of only one explanation. Your alchemist was hoarding gold as a speculation. He possibly got hold of it illegally. So, being as we all agree a fine goldsmith, he decided to keep it in the form of this vessel rather than ingots of which the origin could be traced.’

That was running close to my early conjecture before I decided on the burial hoard. I said that it seemed an expensive hobby.

The curator, who was probably worried by the rising cost of insuring and guarding his own collection of near-eastern gold, and kept a close eye on the value of priceless objects if stolen and melted down, at once replied to that.

‘It only cost him his time. Weight of your bowl is about 180 ounces. At the beginning of the year the gold price was £600 an ounce. So we can say its value was £108,000.1 don’t know whether the rarity of pure gold would make it more or less. Gold price now is £670 an ounce. Value of bowl something over £120,000. Profit just by sitting still for six months £12,000.’

Then Marrin’s profit on gold, so long as the price continued to rise, would alone account for the prosperity of his commune without any need for the pretence of alchemy. But what started him off when Broom Lodge was bust and he rescued it? He had not the capital to speculate in gold; and even if he could somehow raise enough to buy, perhaps on margin, what would have happened to his precious commune if the price fell?

No, somewhere there was still a mystery. Marrin had suddenly changed from futile and contemplative salmon fishing to working in gold. That, as Elsa had said, brought prosperity. What then was the object in impressing his public by a skeleton glyptodont and a vessel reputed by the inner circle to be sacred? Answer, as Sir Anthony had acutely observed: to hide the source of the gold. Was it fraud in South Africa or a dig in the Severn meadows or dredging the Wigpool lake or some method of transmutation more scientific than alchemy? We were free to choose which impossibility was the least impossible.

At the Museum there was nothing more to be said beyond our expressions of respect and gratitude. The cauldron was restored to its hat box – with even more care than before – and we went back to the major’s club for lunch. In the taxi we laid off the whole subject except once when I exploded:

‘So bang goes your Grail and my Nodens’ treasure! You do agree, Denzil?’

‘With reservations, yes.’

‘You said once that the Grail could be remade.’

‘I said the druidicals thought so.’

‘But you accepted it.’

‘Pure gold. Inspiration. Wasn’t wrong in a way. Give it a rest till after lunch, old boy!’

He was right. The club dining-room was no place for discussion of subtleties apart from those of the wine list. And we needed to be fortified against so much disappointment. Afterwards, in a quiet, cool corner with brandy in front of us, he said: