So long as I avoided curiosity and possible suspicion by showing myself too often in the neighbourhood of Broom Lodge there was no reason why Personality No. 1 should not move freely, apart from the difficulty of changing into him; nor was Elsa accountable to anyone for her absences. So a luxurious double room was booked at Thornbury, safely across the river, for Mr & Mrs Piers Colet and for the first time we were free to make love with abandon, sleep in each other’s arms, eat and drink and laugh together. ‘Get me out of here!’ she had begged me immediately after her uncle’s death, but now she was hesitant, and all she would say in answer to my insistence was, ‘Wait, my darling!’ I supposed that she was moved by a reluctant feeling of duty to the commune. But we were not yet so accustomed to each other that I could make a good shot at the cause of occasional reticence.

While we were walking in the hotel garden, putting off as long as possible the moment of parting, she suddenly asked me:

‘Why do they go to Wigpool?’

‘I think for iron ore, unless they are just having fun underground.’

‘It couldn’t be for iron,’ she said. ‘Uncle Simeon bought the supplies for the blacksmith’s shop. It’s all full of rods and plates already.’

But all the same it could be for the ore. In one way Marrin was no fraud. It was all very well to learn to handle iron, but that scanty remnant of humanity, reborn into the neolithic culture which he foresaw, would not know how to get the raw material.

‘I’m prepared to bet anything that they are mining the iron ore with pick and shovel,’ I said, ‘and somewhere in the Forest are smelting it with coal. Or better! Smelting it with charcoal on the off-chance that our descendants think coal is only useful for chucking at chickens.’

‘Well, they do try to smelt it.’

‘At Broom Lodge?’

‘No. Somewhere in the Forest. I remember he had some leaflets printed inviting schoolchildren to watch a demonstration. It seemed quite innocent and good propaganda for the commune. I did wonder if it had anything to do with their silly sacred ingots, but they come from Wigpool, I think.’

‘What sacred ingots?’

‘They are on a table by the entrance to the lab, and the initiates bless them when they pass. I wish I knew what they are doing at Wigpool.’

‘Easy! I’ll find out and tell you.’

‘But if they find you hanging about?’

‘They won’t. Don’t you bother!’

‘Piers, where are you living?’

‘You know I am always travelling.’

‘Just one hotel to another?’

‘That’s it.’

‘And all of them smell of coal?’

‘Darling, what did you say to me? Wait!’

‘Don’t take risks, Piers!’

‘In search of what? The golden cauldron?’

‘You were taking risks long before that disappeared.’

‘Diving with your uncle?’

‘Where’s his second suit, Piers?’

‘Offered to Nodens, I expect.’

‘They do offer things to somebody,’ Elsa said.

‘How do you know?’

‘Piers dear, I don’t know how I know. I watch their faces as I’ve watched yours. And I wonder. And when things are missing I ask questions and get answers I don’t believe.’

‘What sort of things?’

‘Animals and flowers and … diving suits?’

‘And you think the altar is at Wigpool? Then they have the cauldron there!’

‘They might have. But, Piers, please, no!’

When we had gone our separate ways, I recrossed the Severn Bridge and left my car in a public car park at Chepstow. With such a number of tourists on their way to and from South Wales or the valley of the Wye the park was always full of cars, and mine was safely lost among them. In any case no one at Broom Lodge except Elsa knew its number. I then took a bus into the Forest and so by footpaths across country to my den.

I had been underrating Elsa’s powers of observation, partly because she was so young, partly for her lack of interest in the religious aspects of Broom Lodge. But she was ageless woman all through, sensitive to discordancies of collective mood or individual deviations from the norm, even if as slight as a change of wind in woodland. She was content to notice without seeking, as I would, at once to explain.

Nodens had turned up several times as if he were a patron saint of the colony. Natural enough. His temple dominates the Severn and the Forest, and I am surprised that early British bishops did not build a church on the hill top and dedicate it to St Nodentius, martyr and miner, whose head was cut off by the prefect of the port, kippered in salmon oil and thereafter able to heal the sick.

In fact the inscriptions show that he was greatly honoured by the Romans, who always recognised a useful god when they saw one. The river and the Forest were his, and his specialities were healing and finding lost property.

Writing those words has suddenly illuminated that curious incident of the lost watch. Carver was perhaps not looking up to heaven to see if there was a magpie in the branches above him; he could have been sending up a prayer of thanks to Nodens.

I have some sympathy for what was genuine in Marrin. Nodens could well have been an ancestral hero, older than Romans or Celts, who in time became a god. It’s a pleasant thought (for which I have no evidence whatever) that he might have been the marine engineer who planned the voyage of the great stones of Stonehenge all the way round Wales, across the Severn estuary and up the Avon.

Such practical details of life in the past fascinated Marrin as they do me. That is why we got on easily together. It is also why he desperately wanted me out of the way. Our interests were close enough – though his crazily extended from past into the future – for him to be afraid that my specialised knowledge might expose the secret of how he financed his colony.

The smelting of iron ore seemed a good point at which to start investigation. So next day I decided to be a private eye and play the major’s game of calling at pubs on the northern side of the Forest. In order to appear businesslike I used my car and Personality No. 1, carrying 2’s outfit in case of need. What I wanted to know was where I could buy a quantity of charcoal. At the big factory, I was told, which supplied the chemical industry. But did anybody still burn charcoal by the old method? Yes, two enterprising ex-miners were hard at it and coining money, though you wouldn’t think it to look at ’em. They had developed a new and profitable market: the suburbs of the larger towns within easy reach where families had fallen for the new craze of outdoor barbecues.

And so to the fairy-tale scene of a charcoal burner. The pyramid of wood smouldered under its bee-hive cover of turf and clay, pouring out trickles of smoke from the vent holes. Alongside the oven were stacks of beech and oak, and a hut where one of the partners was always on duty day and night. Apparently a charcoal pit is more of a nuisance than a baby. It must be inspected every two hours in case it bursts into flame; and there is only one way to build the shallow pit which contains the bee-hive. That is to learn it from your father who learned it from his father.

All this the burner on duty told me, a cheerful grin splitting his black-dusted face, evidently pleased to have company. I arrived at the point which interested me by saying that I couldn’t understand how charcoal could produce enough heat to melt iron from the ore, and got the most suprising answer.

‘Cor! Shouldn’t a believed it meself! But now ‘ee canst go see it done. Customers of mine they are. ‘Eathen Mohammedans, I’m told, but no ‘arm in ’em. All live together and do everything as it ain’t done no more. Now, if ’ee ‘urries –’ he pulled out a printed sheet from his pocket and consulted it. ‘Aye, there’s frying today! Nip on down to Flaxley Woods, and you’ll catch ’em at it twixt road and stream.’

I knew exactly where he meant and hurried, after changing in the car to Personality No. 2. Car and 2 were not supposed to be seen together, but the risk was small and any future developments seemed likely to call for No. 2 and his feet. Not far off the road was a quarter circle of low cliff left by ancient diggings, and below it open grass where time and the rains had smoothed spoil from the mine into a bumpy amphitheatre. There a furnace had been built of uncut stones mortared with clay. Near it was the Broom Lodge van containing sacks of charcoal.