‘World ill-health is like world hunger,’ said Lady Helena. ‘We could end both tomorrow if we wanted to.’ And she’d become terrified of the potential abuse. ‘Imagine what the military industrial complex would do with animal hybrids,’ she said. ‘Better that the knowledge dies with me.’

Nightingale glanced my way and gave his head the almost imperceptible tilt that meant it was time for the children to wander off and entertain themselves. I had a number of incentives lined up to coax Caroline away, but in the end I just asked if she wanted a tour and she said yes.

We were followed by Toby, who’d shaken off his sugar induced lethargy and had obviously decided that he wanted a bit of attention.

I started with the lecture hall, where generations of practitioners had snoozed their way through demonstrations and lectures, then the smoking room with its art nouveau trimmings and into the mundane library where we could slip up the ladder to the top stacks and step through a concealed doorway onto the landing. Then up another flight of stairs to the main lab.

‘What are you doing here?’ asked Caroline.

I had a pile of modified first generation smartphones at one end of the lab and a noticeably scorched sheet of metal on a bench at the other end. I’d painted distance markers on the metal and on the floor around it. The remains of a couple of cheap pocket calculators were still welded to the innermost markers – I hadn’t had a chance to scrape them off yet.

‘Remember when the lights went out at Harrods?’ I asked.

‘I remember your master knocking me off my feet,’ she said.

‘He’s not my master,’ I said.

‘Well he’s not your dad, is he?’ said Caroline and then looked at me sharply. ‘He’s not, is he?’

‘He’s my boss,’ I said. ‘My governor.’

‘I see,’ she said. She looked at the bench. ‘Magic interferes with technology – do you know why?’

‘No,’ I said. ‘Do you?’

‘No,’ she looked at the pile of smartphones. ‘But I think you know more than I do.’

So I explained that, as far as I could tell, magic had a serious degrading effect on microprocessors, and a lesser effect on transistors. ‘But not on thermionic valves,’ I said, ‘or simple circuit boards.’

‘I know about that,’ she said and held up her wrist to show off a silver stainless steel Classic Ladies Fireman from Balls – which was at least eight hundred quids’ worth of watch.

‘I’ve shown you mine,’ she said, so I held my wrist to show my black and silver Omega.

‘Damn,’ she said and grabbed my forearm and pulled it up for a closer look, ‘Where did you get this?’

‘Christmas present,’ I said.

‘What about your boss?’ asked Caroline. ‘Your guvnor? What’s he got?’