‘Excuse me,’ I said in my best policeman voice. ‘Could I have a word?’ They actually teach you how to do the voice at Hendon. The aim is to achieve a tone that cuts through whatever fog of alcohol, belligerence or randomised guilt the member of the public is floating in.

The young man ignored me. He pulled a second spray can from his jacket pocket and began shading the edges of a capital E. I tried a couple more times but he seemed intent on finishing the word EACH.

‘Oi sunshine,’ said Lesley. ‘Put that down, turn round and talk to us.’

The hissing stopped, the spray cans went back in the pockets and the young man turned. His face was pale and angular and his eyes were hidden behind a pair of smoked Ozzy Osbourne specs.

‘I’m busy,’ he said.

‘We can see that,’ I said and showed him my warrant card. ‘What’s your name?’

‘Macky,’ he said and turned back to his work. ‘I’m busy.’

‘What you doing?’ asked Lesley.

‘I’m making the world a better place,’ said Macky.

‘It’s a ghost,’ said Abigail incredulously.

‘You brought us here,’ I said.

‘Yeah, but when I saw him he was thinner,’ said Abigail. ‘Much thinner.’

I explained that he was feeding off the magic Lesley was generating, which led to the question I always dread.

‘So what’s magic, then?’ asked Abigail.

‘We don’t know,’ I said. ‘It’s not any form of electromagnetic radiation. That I do know.’

‘Maybe it’s brainwaves,’ said Abigail.

‘Probably not,’ I said. ‘Because that would be electrochemical and it would still have to involve some kind of physical manifestation if it was going to be projected out of your head.’ So just chalk it up to pixie dust or quantum entanglement, which was the same thing as pixie dust except with the word quantum in it.

‘Are we going to talk to this guy or not?’ asked Lesley. ‘Because otherwise I’m going to turn this off.’ Her werelight bobbed over her palm.

‘Oi Macky,’ I called. ‘A word in your shell-like.’

Macky had returned to his art – finishing up the shading on the H in EACH.

‘I’m busy,’ he said. ‘I’m making the world a better place.’

‘How are you planning to do that?’ I asked.

Macky finished the H to his satisfaction and stepped back to admire his handiwork. We’d all been careful to stay as far from the tracks as possible but either Macky was taking a risk or, most likely, he’d just forgotten. I saw Abigail mouth Oh shit as she realised what was going to happen.

‘Because,’ said Macky and then he was hit by the ghost train.