New Row was a narrow, pedestrianised street between Covent Garden and St Martin’s Lane, with a Tesco’s at one end and the theatres of St Martin’s Lane at the other. Tokyo A Go Go was a bent place halfway down, sandwiched between a private gallery and a shop that sold sporting gear for girls. The interior was long and barely wide enough for two rows of tables, sparsely decorated in minimalist Japanese fashion, with polished wooden floors, tables and chairs of lacquered wood, lots of right angles and rice paper.

I spotted Nightingale at a back table eating out of a black lacquered bent box. He stood when he saw me and shook my hand. Once I’d settled myself opposite, he asked if I was hungry. I said no thank you. I was nervous, and I make it a rule never to put cold rice into an agitated stomach. He ordered tea, and asked if I minded if he continued eating.

I said not at all, and he returned to spearing food out of his bent with quick jabs of his chopsticks.

‘Did he come back?’ asked Nightingale.

‘Who?’

‘Your ghost,’ said Nightingale. ‘Nicholas Wallpenny: lurker, bug hunter and sneak thief. Late of the parish of St Giles. Can you hazard a guess as to where he’s buried?’

‘In the cemetery of the Actors’ Church?’

‘Very good,’ Nightingale said, and grabbed a duck wrap with a quick stab of his chopsticks. ‘So, did he come back?’

‘No he didn’t,’ I said.

‘Ghosts are capricious,’ he said. ‘They really don’t make reliable witnesses.’

‘Are you telling me ghosts are real?’

Nightingale carefully wiped his lips with a napkin.

‘You’ve spoken to one,’ he said. ‘What do you think?’

‘I’m awaiting confirmation from a senior officer,’ I said.

He put the napkin down and picked up his teacup. ‘Ghosts are real,’ he took a sip.

I stared at him. I didn’t believe in ghosts, or fairies or gods, and for the last couple of days I’d been like a man watching a magic show – I’d expected a magician to step out from behind the curtain and ask me to pick a card, any card. I wasn’t ready to believe in ghosts, but that’s the thing about empirical experience – it’s the real thing.

And if ghosts were real?

‘Is this where you tell me that there’s a secret branch of the Met whose task it is to tackle ghosts, ghouls, faeries, demons, witches and warlocks, elves and goblins … ?’ I said. ‘You can stop me before I run out of supernatural creatures.’

‘You haven’t even scratched the surface,’ said Nightingale.

‘Aliens?’ I had to ask.

‘Not yet.’

‘And the secret branch of the Met?’

‘Just me, I’m afraid,’ he said.

‘And you want me to what … join?’

‘Help,’ said Nightingale, ‘with this inquiry.’

‘You think there’s something supernatural about the murder?’ I asked.