I had no objection. If I didn’t turn up by seven-thirty it could mean that I wasn’t going to turn up at all. Her vague fears had made me take this simple expedition rather more seriously. I remembered that I had only been as far as the major’s temporary bed-sitting room and did not know what was in the darkness beyond. The ingenuities of the late Simeon Marrin were not to be despised.

I showed her where she was to meet me – the lair in the foxgloves from which I had kept watch on the back of Broom Lodge – and settled down there to eat some sandwiches and wait for her signal.

A little after three the tablecloth was waved – a long enough wait to show me that she had made a thorough check of suspects and occupations. I returned to the car, changed to the shabbier Personality No. 2 and drove off to Wigpool. No tea and buns were being served at the Methodist Chapel and there were no cars outside, so I had to look for some other discreet parking place, not too far away. I passed no one in my walk to the rising ground above the shaft, but when I lay down and looked over the edge, I found that a tractor was travelling back and forth over the pasture between slope and woodland, cutting thistles, and that I should be in full view of the driver when I dismantled the pile of pit props and entered the shaft. It was no wonder that the ‘geologists’ only went to work when dusk had closed down work on the land and no farm hands or ex-miners full of professional curiosity were likely to stroll up and ask questions.

When the tractor drove away, I cleared the pile of props and went down. All was silent. There were more tracks in the mud than on my previous visit, but only of one person coming and going. It looked as if someone had gone down to see that the obstinate major was all right, and to supply him with food and drink. No light came from the bay which he had occupied. I quickly flashed my torch on the interior, fearing the worst, and was relieved to see him sound asleep under blankets on a mattress against the wall.

I called softly:

‘Denzil!’

He turned over and replied in the words of the young Samuel:

‘Speak, Lord!’

I said it was only me but that he could get up and gird his loins all the same.

He unrolled himself. His unshaven face, set but smiling as if I was being most courteously welcomed to Mess, though they were just out of battle, made me realise that I loved the ridiculous man as Arthur might have done, had done, would do. These time-travellers of imagination play the devil with one’s tenses.

‘You’re taking a bit of risk, old boy,’ he said.

‘None at all. I left the entrance open and we can clear out now.’

‘I told you…’ he began.

‘I know. But I give you my word of honour that the Grail is not here. Elsa has it.’

‘You have seen it?’

‘Yes,’ I lied. ‘And at last we can go to the experts with it and find out how old it is and whether what you believe is possible.’

‘Good! And before we go we will find out what else these devil-worshippers have.’

He explained that when he was left alone he had explored as far as the lake – yes, there was a black lake – but could see no further with the wretched lamp which was all the light they had allowed him. Now with my powerful torch it would be worth having another look. He knew from snatches of talk and a glimpse of Evans in a blue robe that some kind of pagan worship took place in the depths.

I doubted if there would be anything of interest except some home-made altar, but then my damned obsession with ancient economies took over. I did want to see where and how they were mining tin. Had there ever been a trade in tin from the Forest of Dean? If there had been were there already ports on the Severn Sea before the iron age and the trade of the Celtic ironmasters? It was now only five o’clock. We had time in hand for a short expedition and had only to follow the footsteps until we came to the working surface, if any. The passage dipped sharply, and where it ended old galleries led off to right and left. That was as far as the miners had gone before abandoning the pit. The air was still good, but probably they were getting too far from the surface for easy working and decided to exploit another of the many possible sites in the Forest where the extraction of the ore more resembled quarrying than mining.

The left-hand gallery ended at a pool. This was the water which had reflected the light of the major’s lamp, but it was not a lake. Footprints led down to the edge, indicating that it could easily be waded, but there was no obvious way out on the other side. As soon as we took to the ankle-deep water we found that the pool was crescent-shaped, passing round a buttress of rock. There the cut gallery stopped, and a natural cave began. No doubt prospectors or the curious had at some time gone beyond the pool and found nothing to encourage a further search for ore; so the account of what they had seen dissolved over the years into mere rumour.

When we had splashed round the corner and on to the ledge at the far side of the pool, footprints occasionally reappeared. We were on an irregular terrace tilting towards the dry bed of a stream, though there was no obvious source for it except the pool itself which presumably became a powerful spring head in winter or after heavy rain. This passage in the limestone, its roof varying in height with small stalactites hanging down, continued for about a hundred yards and suddenly opened into a spectacular high-domed cavern.

The beam of my torch searching the flattish floor at once showed up what the major anticipated. At the east end of this cathedral – I have no idea whether in fact it was east – and near the brink of the lake stood an altar. One couldn’t call it a rough altar, for the craftsman Marrin had been at work. The ashlars were smooth and evenly jointed. At the back was a little dais of polished stone which could only be intended for the golden cauldron. I could visualise how the concave curve of the sides would precisely merge into the swelling curve of gold.

In front of the altar was another of Marrin’s fantasies: a pattern of two concentric circles delineated by fragments of shining, white quartz cemented to the floor, the space between the circles so closely filled with figures picked out in variegated stones that one could almost call it an amateur mosaic. As well as the signs of the zodiac I recognised a number of Mithraic symbols – not surprising since all the mystery religions borrowed from each other. More sinister than this priestly play with pebbles was the surface of the altar. A channel led across it, suggesting the sacrifices which Elsa had suspected. I had seen on classical altars such channels to carry away the blood. Here, too, there was a thin, dark streak descending to the ground.

Halfway down the cavern the rumoured lake began. It was fed by a small stream trickling in over a smooth glacis from a recess low in the right hand wall of the cavern and leaving the centre of the lake smooth as a mirror. The black water extended under the gradually lowering roof until they nearly met. I could not look at this grinning mouth without a feeling of mistrust, not that dragons or Gwyn ap Nudd were expected suddenly to break the surface, but I was conscious of the Forest far above and that this was the sink into which the remains of rock, tree and all the two-legged, four-legged life of the light eventually filtered.

Marrin had been determined to extract some of its riches. At the edge farthest from the stream stood a windlass. Two ropes passed out from it, one dipping down into the lake while the roof of the cavern was still twenty feet above it, the other entering the slit between rock and water. An iron dredge, somewhat the shape of a cradle, hung from the windlass. This was evidently a primitive device, well within the capacity of neolithic man, for sampling the bottom of the lake.