Still, I half expected the saint’s statue to be frowning at me, disapproving, as I passed between the iron gates and entered the hushed chapel proper, where the cave-like walls arched up to rest upon the ghostly row of pillars. But when I glanced at Radegonde’s stone face she looked back benignly. Evidently, I thought, even saints could understand the pull of curiosity.

Thierry would be terribly put out when he learned we’d come up without him, but he’d gone to bed before us – it was really his own fault. The Chamonds, too, had given in to weariness, and Jim as well, and François had gone back up to the Clos, to help with Lucie. Which had only left the four of us – Harry, Christian, Neil and me – quite pleasantly awash in Calvados and irretrievably beyond the point of being tired.

I had, for my own part, reached that magical plane of inebriation in which time begins to float and anything seems possible, which went a long way towards explaining why, when Harry had leaned forward and said: ‘Listen, I’ve got an idea …’ instead of running in the opposite direction as experience would warrant, I had donned my jacket and trailed after him. Completely sober, I’d have had more sense. And I would never have come up that cliff path in the dark, alone or no.

‘I’ve got it open,’ Christian announced, twisting the key to the third and final gate. Harry’d wandered down the aisle to stand below the Plantagenet fresco, his torchlight angled up to catch the vibrant figures of young Isabelle and John. ‘Well done,’ he said, in absent tones. He stood a moment longer, looking up. ‘I was afraid it might have changed, since I last saw it.’

I raised my eyebrows. ‘Changed? In one week? Hardly likely.’

‘Not one week, love. It’s been at least two years since I’ve been up here, to the chapelle. Had I known my hiding place was quite so close I might have tried to sneak in another visit. One forgets how very beautiful—’

‘Hold on,’ I stopped him, frowning. ‘You were here last week. You must have been. That’s how I knew that you were missing in the first place – you left your coin, your King John coin, there on the altar, as an offering.’

‘No chance.’

‘You did.’ My chin rose stubbornly. ‘Or at least, if you didn’t leave it there yourself, perhaps the gypsies …’

‘Darling Emily.’ My cousin strolled towards me, hand in pocket. ‘I’m not all that daft, you know. I mean, they’re lovely people, gypsies, but they will take things unless you’re careful. My watch is gone, and my wallet … but they haven’t taken this.’ He held his hand out, with the coin upon it, to show me. ‘With this, I was very careful.’

I stared. It was the King John coin, without mistake, safe in its plastic case. I opened my own wallet, just to be sure, and drew out the matching coin. Harry stabbed it with a beam of light.

‘How curious,’ he said. ‘I wonder how on earth it got there.’

‘I don’t know.’

Christian leaned in closer for a better look. ‘It is very old, yes? Somebody must have found it on the ground here, near the tombs perhaps, and put it with the other coins as tribute to Sainte Radegonde.’

‘Y-yes, I suppose that’s how it could have happened.’

‘You don’t sound terribly convinced,’ said Harry, grinning. ‘What other explanation is there – Sainte Radegonde herself, perhaps? A helping hand from beyond? Don’t tell me that you’ve found religion, Em.’

‘Of course not.’ And I meant it, only … only …

Behind the altar, lovely pale Sainte Radegonde just went on gazing at nothing in particular, her blind, carved eyes serene and peaceful. I put the coin back in her dish of offerings, and pushed it well down, frowning. Neil moved up behind my shoulder, and his breath brushed warm on my neck. ‘The world would be dead boring, don’t you think, if everything were easy to explain?’

My cousin grinned. ‘The true Romantic viewpoint,’ he pronounced. ‘Come on then, are we ready? Tunnels again, Emily. You’ll have to cope. She has a tunnel thing,’ he told Neil, confidingly.

‘Oh, yes?’ Neil glanced my way. ‘I’ll have to remember that.’

Beyond the second gate the glare of harsh electric light seemed almost an intrusion. The chapel caves cried out for candles, I thought, or the flicker of a burning torch. The hanging bulbs and switches took away much of the mystery, and it wasn’t until we’d reached the steep and crooked steps that dropped down to the holy well that I felt again the ancient and eternal sense of wonder shared by all explorers.

Harry must have drunk more than I’d thought. By the time the rest of us had slid with caution down the steps my cousin had stripped neatly to his underpants.

‘What are you doing?’ I demanded.

‘Well, you can’t see anything from here. Just pebbles, really. If I’ve come all this way to see diamonds, then I want to bloody see them, don’t I?’

I looked down at the narrow shaft of clear blue water, plunging several metres deep into the rock. ‘You can’t be serious.’

He just grinned, stepped cleanly off the ledge and dropped feet-first into the well. The spray that came up after him was cold as ice. Neil knelt beside me, one arm braced against the pale stone wall to see I didn’t accidentally topple in myself. ‘We’ll fish him out again,’ he promised. ‘Never fear.’ The three of us peered over the edge, to watch as Harry forced himself towards the bottom, his hands splayed out in search of the elusive diamonds. ‘Runs in your family, does it?’ Neil asked idly. ‘This sort of behaviour?’