And it was while I’d been underground that I’d had what I thought at the time was hallucination. A waking dream that I’d stood on the Oxford Road when it was a ribbon of dust through the countryside and talked to a young man with a sword at his hip and a gleam in his eye. The locals called him Sir William and he wanted me to stay to have a chat but I had business in the land of the living. When I was done with that I enlisted the help of the Folly’s official archivist, Dr Harold Postmartin, to see what the histories said. We tracked down a reference to him in the Rotuli Parliamentorum which as any fule kno is all in Latin – he was listed as Sir William of Tyburn, although the translation could have been read as ‘of the Tyburn’.

I’d have liked to ask Lady Ty whether our young Sir William had been an earlier incarnation of the Tyburn and did she have any memory of him or sense of continuity or was there a total break when he ‘died’ in the mid-nineteenth century.

But it’s a wise man who knows when to keep his gob shut, and so we spent what felt like a really long time in silence until finally Lady Ty’s head jerked round to face the front of the house.

‘Well, that’s you off the hook,’ she said. ‘Your Lord and Master has arrived.’ A couple of moments later Nightingale opened the kitchen door and stepped in. He gave Lady Ty a formal little nod.

‘Cecelia,’ he said. ‘How are you holding up?’

‘Oh, I’m just gratified to be getting the personal touch,’ she said.

‘Why don’t you come with me,’ said Nightingale, ‘and we’ll see if we can sort this out.’

It’s what you say, even to people standing over the bleeding body of their significant other with a claw hammer in their hand. And the weird thing is that most people, even the ones that have got to know that whatever happens it isn’t going to end well for them, come along quietly and let themselves be sorted out.

I didn’t think that Lady Ty was going to stay quiet indefinitely but, sometimes, that’s the joy of being a lowly constable. You get to foist your problems onto your elders and betters.

Before he left the kitchen Nightingale caught my eye and gestured upwards – he wanted me to check Olivia’s bedroom before the main search team got there.