Nightingale has his own attitude to the modern world. If he deems something necessary or useful – modern police communications, for example – he is perfectly willing to learn how to use it. This he does with frightening speed and efficiency, although anyone who’s spent a couple of months mastering a forma will find even the deeper mysteries of the Airwave handset a piece of piss. Still, I wasn’t looking forward to explaining to him the finer points of DNA fingerprinting, not least because I’d forgotten quite a lot of it myself. I was just about to start looking things up on the internet when I realised that it didn’t have to be me that explained it to Nightingale – I just needed to convince Walid, and then let him do all the heavy lifting.

‘Changeling, eh,’ said Dr Walid.

‘A possible substitution,’ I said. I was out on the canteen terrace, which was in full sunlight and no breeze at all, but got the best phone bars in the nick.

‘But not as a child?’

‘As an eleven-year-old,’ I said.

‘That would be a rare thing indeed,’ he said. ‘I’ll talk to Thomas. Once he says yes, I’ll email you instructions as to how I want you to handle the samples.’

Once he says yes, I thought. Walid really wants that changeling DNA.

I heard a mechanical organ playing in the distance and looking over, across the railway tracks and the bypass, I could just see a swirl of movement amongst the trees. I realised it was a Sunday and the Steam Fair was open for business – not just a staging post after all. Very faintly, over the mechanical organ, the traffic noise from the bypass and the thrum of the generators, I could hear the sound of excited children.

How many of those kids would have been kept indoors until now?

Once I was done with Dr Walid it was time to check in with Inspector Pollock, who seemed to think it was time I took the initiative. I pulled out the disposable phone and texted, Talk to me!

‘She’s not going to fall for this, you know,’ I’d told Pollock.

‘You never know,’ he’d said. ‘And it costs us nothing.’

I really hoped so.

While I was waiting to see which train would wreck first, I drove into Leominster proper and put in an order for another twenty detectors on the basis that I could always take them back to the Folly if I didn’t use them. Call Me Al was delighted. I was probably doubling his turnover that month. I thanked him for pointing out the UKUFOindex site and he asked whether I wanted to meet up with him and his mates at the pub later. I said I’d see if I was free.