‘I didn’t know you had an obsessive interest in quartz.’

He gave me one of his blank stares, which I knew didn’t mean that he hadn’t heard or understood what I’d said, but that he didn’t intend to explain.

‘I’m going fishing,’ he said, plunging his arms back into the box.

So the quartz was bait. I put down the porphyry and picked up another piece. It was small, the size of a squared-off egg, and beautiful, as clear and translucent as glass. The label said simply ‘Rock Crystal’.

‘If you want something useful to do,’ said Charles, ‘you can write out what sort they all are on the plain labels you will find on my desk, and then soak the Foundation’s label off and put the new ones on. Keep the old ones, though. We’ll have to replace them when all this stuff goes back.’

‘All right,’ I agreed.

The next chunk I picked up was heavy with gold. ‘Are these valuable?’ I asked.

‘Some are. There’s a booklet somewhere. But I told the Foundation they’d be safe enough. I said I’d have a private detective in the house all the time guarding them.’

I laughed and began writing the new labels, working from the inventory. The lumps of quartz overflowed from the table on to the floor before the box was empty.

‘There’s another box outside,’ Charles observed.

‘Oh no!’

‘I collect quartz,’ said Charles with dignity, ‘and don’t you forget it. I’ve collected it for years. Years. Haven’t I?’

‘Years,’ I agreed. ‘You’re an authority. Who wouldn’t be an authority on rocks, after a life at sea.’

‘I’ve got exactly one day to learn them in,’ said Charles smiling. ‘They’ve come later than I asked. I’ll have to be word perfect by tomorrow night.’

He fetched the second lot, which was much smaller and was fastened with important looking seals. Inside were uncut gem quartz crystals, mounted on small individual black plinths. Their collective value was staggering. The Carver Foundation must have taken the private detective bit seriously. They’d have held tight to their rocks if they’d seen my state of health.