I’d asked Nightingale about this, since he’d been there, but he said hadn’t spent a lot of time at the Folly in those days. Out and about in the Empire and beyond, he’d said. I asked him what he’d been doing.

‘I remember writing a great many reports. But to what purpose I was never entirely sure.’

I didn’t think they were ‘souls’ but until I knew what they were, I was going to err on the side of ethical conduct. I scrapped out a shallow depression in the ballast just where Abigail had made her mark and buried the glasses there. I made a note of time and location for transfer to the files back at the Folly. Lesley made a note of the location of the hole in the fence but it was me that had to call in to the British Transport Police on account of her still, officially, being on medical leave.

We bought Abigail a Twix and a can of coke and extracted a promise that she’d stay off the railway tracks, Hogwarts Express or no Hogwarts Express. I was hoping that Macky’s ghostly demise would be enough to keep her away on its own. Then we dropped her off back at the flats and headed back to Russell Square.

‘That coat was too small for her,’ said Lesley. ‘And what kind of teenage girl goes looking for steam trains?’

‘You think there’s trouble at home?’ I asked.

Lesley jammed her index finger under the bottom edge of her mask and scratched. ‘This is not fucking hypoallergenic,’ she said.

‘You could take it off,’ I said. ‘We’re nearly back.’

‘I think you should register your concern with Social Services,’ said Lesley.

‘Have you logged your minutes yet?’

‘Just because you know her family,’ said Lesley, ‘doesn’t mean you’ll be doing her any favours if you ignore the problem.’

‘I’ll talk to my mum,’ I said. ‘How many minutes?’

‘Five,’ she said.

‘More like ten.’

Lesley’s only supposed to do so much magic per day. It’s one of the conditions laid down by Dr Walid when he signed off on her apprenticeship. Plus she has to keep a log on what magic she does do and once a week she has to schlep over to the UCH and stick her head in an MRI while Dr Walid checks her brain for the lesions that are the early signs of hyperthaumaturgical degradation. The price of using too much magic is a massive stroke, if you’re lucky, or a fatal brain aneurysm, if you’re not. The fact that, prior to the advent of magnetic resonance imaging, the first warning sign of overuse was dropping dead is one of the many reasons why magic has never really taken off as a hobby.

‘Five minutes,’ she said.

We compromised and called it six.