Lesley asked Abigail what she thought she was doing coming down here in the first place.

‘I wanted to see the Hogwarts Express,’ she said.

Not the real one, Abigail was quick to point out. Because it’s a fictional train innit? So obviously it’s not going to be the real Hogwarts Express. But her friend Kara who lived in a flat that overlooked the tracks said that every once in a while she saw a steam locomotive – because that’s what you’re supposed to call them – which she thought was the train they used for the Hogwarts Express.

‘You know?’ she said. ‘In the movies.’

‘And you couldn’t watch this from the bridge?’ asked Lesley.

‘Goes past too fast,’ she said. ‘I need to count the wheels because in the movies it’s a GWR 4900 Class 5972 which is 4–6–0 configuration.’

‘I didn’t know you’re a trainspotter,’ I said.

‘I’m not,’ said Abigail and punched me in the arm. ‘That’s about collecting numbers while this was about verifying a theory.’

‘Did you see the train?’ asked Lesley.

‘No,’ she said. ‘I saw a ghost. Which is why I came looking for Peter.’

I asked where she’d seen the ghost and she showed us the chalk lines she’d drawn.

‘And you’re sure this is where it appeared?’ I asked.

‘He appeared,’ said Abigail. ‘I keep telling you it’s a he.’

‘He’s not here now,’ I said.

‘Course he isn’t,’ said Abigail. ‘If he were here all the time then someone else would have reported him by now.’

It was a good point and I made a mental note to check the reports when I got back to the Folly. I’d found a service room off the mundane library that contained filing cabinets full of papers from before World War Two. Amongst them, notebooks filled with handwritten ghost sightings – as far as I could tell ghost-spotting had been the hobby of choice amongst adolescent wizards-to-be.

‘Did you take a picture?’ asked Lesley.

‘I had my phone ready and everything for the train,’ said Abigail. ‘But by the time I thought of taking a picture he’d gone.’

‘Feel anything?’ Lesley asked me.

There’d been a chill when I’d stepped into the spot where the ghost had stood, a whiff of butane that cut through the fox urine and wet concrete, a Muttley-the-dog snigger and the hollow chest roar of a really big diesel engine.