We worked for some time changing the labels while Charles muttered their names like incantations under his breath. ‘Chrysoprase, Aventurine, Agate, Onyx, Chalcedony, Tiger-eye, Carnelian, Citrine, Rose, Plasma, Basanite, Bloodstone, Chert. Why the hell did I start this?’

‘Well, why?’

I got the blank stare again. He wasn’t telling. ‘You can test me on them,’ he said.

We carried them piece by piece into the dining-room, where I found the glass-doored book shelves on each side of the fire had been cleared of their yards of leather-bound classics.

‘They can go up there later,’ said Charles, covering the huge dining-room table with a thick felt. ‘Put them on the table for now.’

When they were all arranged he walked slowly round learning them. There were about fifty altogether. I tested him after a while, at his request, and he muddled up and forgot about half of them. They were difficult, because so many looked alike.

He sighed. ‘It’s time we had a noggin and you went back to bed.’ He led the way into the little sitting-room he occasionally referred to as the wardroom, and poured a couple of stiffish brandies. He raised his glass to me and appreciatively took a mouthful. There was a suppressed excitement in his expression, a glint in the unfathomable eyes. I sipped the brandy, wondering with more interest what he was up to.

‘I have a few people coming for the weekend,’ he said casually, squinting at his glass. ‘A Mr and Mrs Rex van Dysart, a Mr and Mrs Howard Kraye, and my cousin Viola, who will act as hostess.’

‘Old friends?’ I murmured, having only ever heard of Viola.

‘Not very,’ he said smoothly. ‘They’ll be here in time for dinner tomorrow night. You’ll meet them then.’

‘But I’ll make it an odd number… I’ll go up before they come and stay out of your way for most of the weekend.’