Lady Helena watched Molly approach. She looked interested but not surprised. I wondered, what did she know about Molly? And what had she heard about the internal disposition of the Folly?

Once we were seated, and Molly had poured the tea, Nightingale gave a little formal nod in the direction of our guests and invited them to eat and drink without fear of obligation.

‘Thank you,’ said Lady Helena. ‘But I’m curious as to whether you believe that sort of thing is really necessary.’

‘Between us?’ said Nightingale. ‘Among practitioners I doubt it’s necessary. In the Court of the Rivers or amongst the High Fae I’m not sure I’d be willing to take the chance.’

Lady Helena took a sip of her tea.

‘You don’t think it’s based on an atavistic fear of the feminine realm?’ she asked and, when Nightingale looked politely blank, added ‘Food and sustenance traditionally being a woman’s responsibility.’

‘I have no idea,’ said Nightingale. ‘But I’ve always liked to err on the side of prudence.’

They fenced along these lines for a bit while I had a slice of strawberry lattice tart and Caroline ate two pink angel cakes in quick succession.

‘I gather you were taught by your mother,’ said Nightingale. ‘Was this the usual practice?’

‘I don’t think there was such a thing as a “usual practice”,’ said Lady Helena. ‘My mother was taught by her aunt, and her aunt by a friend of the family.’

‘A female friend?’ asked Nightingale.

‘Naturally,’ said Lady Helena. ‘But I think we may have exhausted that topic – shall we get down to business?’

‘By all means,’ said Nightingale. ‘What would you like to discuss?’

Lady Helena put her tea down – she’d barely touched it.

‘Jonathan Wild’s Ledger, The Third Principia, alchemy, the secret of eternal life.’ She smiled – a bright echo of the young woman in the photograph. ‘Is that enough to be going on with?’

‘We’re always interested in information leading to the recovery of stolen goods,’ said Nightingale.

‘Is that the case here?’ asked Lady Helena.

Nightingale glanced my way.

‘The Third Principia was definitely stolen in 1719,’ I said. ‘The Master of the Royal Mint at that time was one Sir Isaac Newton, who was busy sending counterfeiters and coin clippers to the gallows for crimes against the currency.’

‘Stolen by Jack Shepherd himself according to legend,’ said Nightingale. ‘So, yes, I believe it counts as stolen property.’

Lady Helena held up her hand to surrender the point.

‘We are both the true heirs of Isaac Newton,’ she said. ‘Whether you’re willing to recognise it or not. We can’t ignore each other and I’m sure you’ll agree that any conflict between us would be both pointless and counterproductive. Which leaves us where?’

Nightingale nodded slowly.

‘You think we should work together,’ he said and then he looked at me and laughed. ‘A stakeholder engagement,’ he said.