Nightingale thought it was an eminently sensible idea, notwithstanding the fact that neither of us had ever done a formal Falcon assessment before, me because I was too junior and him because in his day such things as assessments and regular case reviews hadn’t been invented. At least, not at the Folly they hadn’t.

‘I don’t even know what I’m supposed to be looking for,’ I said.

Nightingale replied that he would immediately repair to the library and see what he could dig up in the way of rural supernatural crime.

‘And I shall call Harold,’ he said. ‘This is just the sort of thing he lives for.’

Professor Harold Postmartin being the Folly’s archivist, amateur historian and Oxford don voted least likely to get a four-part documentary series on Channel Four, six years in a row.

‘And now that I think of it,’ said Nightingale, ‘it might be worth reaching out to some of our other friends in the demi-monde. Just on the off-chance.’

So I glumly reported back to Edmondson and Windrow that not only would the SAU be happy to do a full Falcon assessment, but we would be tasking our senior civilian analyst and drawing on our covert human intelligence sources – even if some of them weren’t entirely human.

They were so delighted they put me in Edmondson’s office down the hall which, quite apart from having its own dedicated HOLMES II socket, was out of sight of the main inquiry office. There was a brief delay while Windrow got my access enabled and rustled up a HOLMES-enabled laptop I could use before they closed the door and let me get on with it.

But get on with what?

Part of the problem with doing a Falcon assessment is that it’s hard to apply professional best practice to a field of law enforcement that most police wouldn’t touch with a one metre extendable baton. Not to mention that the closest the Folly had come to a formal assessment were the times we’d had to tell a senior officer that having occult graffiti sprayed across the crime scene did not make it a Falcon case. Especially if the symbols had been cribbed from Aleister Crowley, The Lord of the Rings or Adventure Time. The only case like that we ever hesitated over was the kanji characters sprayed onto the front of a private school in Highgate, but according to one of Postmartin’s friends at the School of Oriental and African Studies they were from a JRPG called Sakura Wars – very popular in the 1990s.

The problem was that once the government pushed through its major cuts in policing, a lot of officers had got the notion that they might be able to unload anything even vaguely weird onto us.

‘Although it is noticeable,’ Nightingale had pointed out, ‘that this never happens if the officer concerned has worked with us before.’