‘Stuff,’ said Beverley. And then she put her arm around my neck and kissed me. It went on for a while too – there was some tongue in there and everything. Things might possibly have got a bit impromptu, if not alfresco, except she let go of me and laughed.

‘What we’re standing on is a limestone ridge,’ she said. ‘Silurian limestone, as a point of fact. Very permeable, the rain goes right through it and down to the river valley where it belongs, leaving up here nice and well drained – hence the buttercups and the harebell along the hedges.’ She put her hands on her hips and cocked her head to one side. ‘Helpful?’

‘Interesting,’ I said.

We followed the path down the heavily wooded slope, past trees that Beverley identified as yew, elder and some oak. I set up another detector where the footpath reached the cleared area which marked the start of the Pokehouse Wood. While I did that, Beverley wandered out into the stands of foxglove that stood between the newly planted saplings. When I’d finished inputting the location I turned to find her gone.

I called her name and she rose out of the nodding purple flowers, the hot sunlight making amber highlights on the strong curve of her upper arms and her neck. I felt a mad rush of desire, not just sex but something wilder and stronger and almost like worship. I wanted to carve statues of her and paint her image on the walls of my cave, where the firelight would make them flicker and jump. I wanted to wrap myself in an animal skin and dance around the campfire wearing a necklace of bear teeth. Had she just asked, I’d gladly have gone mammoth hunting in her honour – although I’d only do that armed with a suitably high-powered rifle. There are limits, you know.

There was definitely power in that place, wild and weird and fae.

‘Did you feel that?’ I asked Beverley.

‘Feel what?’ she asked.

I took a deep breath. It’s observable but not reliably observable. It can have a quantifiable effects, but resists any attempt to apply mathematical principles to it – no wonder Newton kept magic under wraps. It must have driven him mental.

Or maybe not – the guy had spent almost as much time on calculating the mystical dimensions of the Temple of Solomon as he had developing the theory of gravity. Maybe Newton liked his life compartmentalised, too.

Hugh Oswald had claimed that Nightingale’s old friend David Mellenby had found a way to close the gap between Newtonian magic and quantum theory. What might have happened if that had been true, what kind of future had died during that terrible rout from Ettersberg?

‘You want to know something strange?’ asked Beverley.

‘I don’t think mammoth goes well with palm oil,’ I said.

She hesitated, and then took that as a ‘yes’.