And I did try, really I did. I swirled and sniffed and scrutinised, and in truth I very nearly saw the purple edge that Armand said was such a telling characteristic of his clear red wine. But when he spoke of complex structure and of ‘legs’, and breathed the scents of strawberries and vanillan oak, I had to admit my own deficiencies. It was a lovely wine, I thought, a great one even, but to my untutored palate it tasted … well, like wine. And the more I drank the more like wine it tasted.

Neil knew. His eyes touched mine and held, smiling, and the faintest shiver crawled between my shoulders.

‘Cold?’ Paul checked, missing nothing. He was well into the fourth vintage. Paul, I felt sure, could see with ease the violet edge, and catch the scent of strawberries. I shook my head, and shrugged to clear the shiver.

‘No, not really.’

Simon looked at Armand, his expression casual. ‘How old,’ he asked him, ‘would your cellars be?’

Armand shrugged. ‘Older than the house. Our cave, our cellar, it was once used by the kings who stayed at the château.’

Paul eyed his brother warningly over the rim of his wine glass, but Simon had already seized the opening. ‘Really? So this was connected to the château, somehow?’

I might have imagined the flickering glance François sent his employer, and the careful pause before Armand replied. ‘Yes. The kings built many souterrains, or tunnels, as you call them. Ours is among the oldest, I believe.’

‘It still exists?’ Simon feigned surprise. ‘You mean you have a tunnel that goes straight to the château?’

Before Armand could answer that, Neil set his own glass on the table. ‘I haven’t seen the souterrain in years,’ he said. ‘Perhaps, Simon, if you ask him very nicely, Monsieur Valcourt will show it to us.’ There was a sort of challenge in his voice, and in the way his level eyes met those of our host.

‘It is kept locked,’ Armand said, finally.

Neil smiled his quiet smile, and the challenge became a dare. ‘Surely, just this once.’

There was a moment’s silence, then Armand’s mouth hardened and he picked the gauntlet up. ‘Why not?’ He turned to François. ‘Do you have the keys?’

I would have preferred not to go with them. The cave, at least, was brightly lit and full of air, and I could half convince myself I wasn’t underground. But once again, I didn’t have much choice. The others swept me with them, through the cave and past a small group of incurious workmen, to a darker narrow passageway behind.

Above our heads the pallid rock, its surface scarred and pitted by the chisels of ancient craftsmen, closed round us like a tomb. The smell of damp was stronger here, and Neil was forced to duck his head. There were at least a dozen doorways bolted shut on either side of the passage.

Simon stopped, excited, at the first one. ‘Is this the entrance to a tunnel?’

‘No.’ Armand laughed, and shook his head, it is a … how do you call it? A broom cupboard. This,’ he told us, walking a few steps on and fitting his key into a lock, ‘this is the door you want.’

The tunnel was just that – a tunnel, hung with cobwebs, strewn with dirt, and smelling of decay. I took one look and stepped back hastily, bumping into Neil. He kindly took no notice.

‘But it’s stone,’ said Simon. He sounded disappointed, and I realised he’d expected to see walls of earth or clay. One didn’t, as a rule, dig holes in solid rock to bury treasure. ‘Is it stone all the way through?’

Armand assured him that it was.

‘Can I go in?’

‘I am afraid,’ Armand replied, ‘that I cannot allow it. This souterrain is old, and there is now a road overhead that weakens it. To use it now would not be wise.’ He swung the door shut and the key in the lock clicked firmly. ‘It is not safe.’

Nothing underground was safe, I thought. It was a relief to surface once more into sunlight, and to feel the whisper of the wind upon my face. I stood a moment enjoying the sensation, while the boys walked on ahead with Neil. Armand hung back as well, his face expectant. ‘So, how do you like my vineyard?’

I told him it was fascinating, and he looked pleased. ‘It is my pride, you understand. This estate has come to me from many generations of Valcourts, and one day it will belong to Lucie.’ He looked out, as I had done earlier, across the flat-topped vines. ‘The greatest part of me lies in this place,’ he told me. ‘I’m glad it fascinates you.’

Simon turned ahead of us. He appeared to have recovered quickly from his setback in the cellar, and having ruled out Armand’s tunnel as a hiding place for Isabelle’s lost treasure, he was eager to get on to other things. He beckoned me impatiently. ‘Emily, come on. We’re going to the Echo next.’

Armand’s eyes narrowed, sliding sideways. ‘He has much energy, that young man.’

‘Yes.’ I couldn’t help the smile. Armand walked with me to the gates, and after a confusing criss-cross of handshakes and thank-yous, he turned to take my hand.

‘You must come back another time.’ Alone, his dancing eyes said, and his smile was a sinful thing. ‘And you must tell me how you enjoy seeing our Echo. It is quite unique.’

I wasn’t entirely sure how one could see an Echo in the first place, but everyone promised me that it was indeed possible, and that there was a lovely view from the Echo, and that I would be suitably impressed.