‘And not come out.’

‘I think that if I returned the cauldron…’ Elsa began.

‘Good girl!’

‘And if I could return it in such a way that you had your miracle…’

‘Better and better!’

‘Pity it won’t float,’ I said, ‘but we might send it over the river in a toy boat.’

He was really angry with me now.

‘Not a game! It’s not a game at all. There must be true reverence.’

‘For a fraud?’

‘For what it creates. Simeon knew that.’

‘Don’t fuss, Piers!’ Elsa ordered me. ‘You aren’t the bloody inquisition. Dear Denzil, are you sure you can make them start training to be goldsmiths?’

‘No. But you can.’

‘How long must I stay?’

‘A week should do it. What do they call that thing which turns one stuff into another? A catalyst, that’s it. Well, you’re the catalyst.’

I was frankly shocked, but realised that with St Elsa’s help our fifth-century Paladin might be able to pull off his revolution. The druidicals were in disarray. Their high priest had died; his successor had been drowned; the gods were angry. While the rest of the commune was indifferent to any nonsense they might get up to, the major at least showed a sign of sympathy by his shaven head.

Denzil no longer believed that the cauldron was the Grail, but he did in some sense believe that its shape and its strange gold partook of the ancient myth. That was what the druidicals, encouraged by Marrin, had believed. So the violently heretical Christian and the pious pagan could agree on its sanctity so long as neither insisted on exact definitions.

Take my old friend Nodens as a half-absurd example. Whether I call him Nodens or an angel makes no difference to anybody. The essential is that I do not wholly deny a Something Else able to influence me. On that Something Else a fifth-century missionary could build, whereas he would have been helpless before a pure materialist – who didn’t exist anyway.

This attempt to comprehend the incomprehensible major by way of Nodens brought the god to mind. Spirit of land and river, healer, restorer of lost property and in his relations with me undoubtedly a god of mischief, he should find a miracle within his powers. Summoned by my thought of him, he remarked – as always through my imagination – that druids were not likely to be familiar with diving and it might be possible to stage a marvel more convincing than a toy boat – or a stone one if it came to that.

The major hurried back to his secular duties, which he was taking very seriously. He only knew a little about agriculture and nothing whatever about the crafts, but his military life had taught him that discipline can be imperceptible. He made no attempt to replace that benevolent dictator, Marrin. He merely organised committees and stood back.

‘You shouldn’t have been so rough with him,’ Elsa said. ‘You know he’s crackers.’

‘He’s not crackers. You just have to decide which century his memory is in while the rest of him is here and now. One half sees pets. The other half commits burglary.’

‘Anyway he saw how we could get rid of our gold before you did.’

‘If he can get his amateur alchemists to work. And that depends on the miracle.’

‘But I’ve made our fortune, Piers! And you aren’t excited, just dreaming.’

‘I am wondering what can give me the exact time when half the blasted Severn is going uphill to Gloucester and the other half going downhill to the Shoots and it’s high water at the Box Rock. Nodens and I will then produce a miracle while you, sweet St Catalyst, do your vestal-virgin stuff on the bank. So back to London and get the Grail out of pawn!’

I have an old friend whose hobby is vintage cars. By day he is an archaeologist, at night a motor mechanic. It seems to be a point of honour that one must rebuild every part as it originally was. To put in a new engine, new gearbox or anything new is as disgraceful as to salt a dig with bones which don’t belong to it. Consequently his workshop is a museum of bits and pieces.

I called on him with Elsa. It was the first time she had appeared to a normal friend in my normal life. She was looking as innocently alluring as an advertisement in a Sunday supplement and he couldn’t take his eyes off her.

‘I want a thin steel rod,’ I told him, ‘painted black and about ten feet long, firmly fixed to a plate at one end with a quick release clamp at the other.’

‘What has the clamp got to take?’

‘The bottom rim of this, and it had better be padded.’

I took the cauldron out of its hat box and showed it to him.

‘What an exquisite thing!’ he exclaimed. ‘Persian and about sixth century B.C., I would say.’

I was glad of that. It showed that a better authority than I could be taken in. I had been feeling a litle humiliated since the verdict of the British Museum.

‘It’s only a modern replica. Gold-plated lead.’

‘But what for?’

I was momentarily stuck for a lie, but Elsa was not.

‘My cousin’s birthday,’ she said. ‘They’re filthy rich, jet set and all that. So I had to have something original.’

He looked at me ironically as if wondering how a serious economist could have got mixed up with a crazy bunch of conspicuous consumers.

‘I’ve got a bit of just the right rod. Strong as a Toledo blade. Come and have a look at it, Piers!’

He led me through a pool of oil round the back of a vast landaulette.

‘So you’ve been out baby-snatching! What a stunner! She looks like the Dea Roma on holiday.’

‘I’m the baby more often than not.’

‘Where did you find it?’

‘Salmon fishing.’

‘Not your style unless you were trying to find how much Julius Caesar paid for a pound. When does she want this device of hers?’

‘As soon as possible.’

‘She would! Well, it’s all straightforward except for the quick-release clamp. I’ll have to look around for that.’

‘And you must let me make a subscription to your old-age pensioners.’

‘It won’t be expensive. But this one would be grateful, wouldn’t you?’ He slapped the glossy flank of the landaulette. I wonder he didn’t blow up its nose.

When we were home again (what enchantment to be able to write ‘home’ instead of ‘my flat’!) Elsa’s curiosity was of course unbounded, but I refused to tell her what I was planning.

‘Because I need your inspiration when you see it for the first time. That’s decisive – far more important than anything else. Is it a miracle or is it not? If there’s any doubt, we’ve had it and you might be in trouble.’

She accepted this nobly and I was allowed to spend a few evenings in the home for senile motors, making a light raft with a float attached to each side to keep it level. When the ten-foot rod was ready, with its plate at one end and its clamp at the other, I tied the lot on top of my car, recovered the cauldron from the bank and told Elsa it was time to go down to Gloucester.

‘Oh, not Gloucester again!’ she exclaimed.

‘Well, the Thames is too crowded. But up the Severn somewhere we ought to find a bit of peace in the dusk.’

‘Thank God it’s not that horrible tideway!’

‘Not yet. And if all goes well and you approve, we’ll stay the night and have a conference with the major next day.’

The map suggested that the Haw Bridge, some six miles above Gloucester, might do for the rehearsal of my experiment. When we got there, the evening river was not so peaceful as I expected, so we walked along the bank carrying with us the raft, the rod, the hat box and all my equipment for diving until we found a spot a little upstream from the bridge where no pleasure cruisers were moored and there was a good screen of bushes between the tow path and the fields. I asked Elsa to cross the bridge, follow the far bank until she was opposite to me and then to watch the gently flowing current and report what she saw.

Meanwhile I changed and assembled the miracle – a mere matter of screwing to the centre of my raft the plate at the bottom of the rod and clamping the cauldron to the top. Then I pushed the raft out to deep water and reduced the pressure in the floats until the rim of the cauldron was just awash.