Suddenly I was struck by the fact that I wasn’t talking to a complete personality. The way the accent bopped around from era to era, the bizarre switches in motive and behaviour. This wasn’t Henry Pyke, or even Mr Punch, this was like a patchwork, a personality cobbled together from half-remembered fragments. Maybe all ghosts were like this, a pattern of memory trapped in the fabric of the city like files on a hard-drive – slowly getting worn away as each generation of Londoners laid down the pattern of their lives.

‘You’re not listening,’ said Lesley. ‘Here I am, taking time out of my busy schedule to gloat and you’re in a world of your own.’

‘Tell me, Henry,’ I said. ‘What were the names of your parents?

‘Why, they were Mr and Mrs Pyke, of course.’

‘And their first names?’

Lesley laughed. ‘You’re trying to trick me,’ she said. ‘Their names were Father and Mother.’

I was right – Henry Pyke, at least the portion of him inside Lesley’s head – was literally not all there.

‘And tell me all the good things that come into your mind,’ I said, ‘about your mother.’

Lesley cocked her head to one side. ‘Now you’re just taking me for a fool,’ she said. She gestured at the principal cast, who’d been impassively watching our exchange. ‘Do you know what The Times said about this production?’

‘It was gloomy and pointless,’ I said as I got to my feet. If Lesley was going to monologue, I was going to use the opportunity to get up.

‘Close,’ she said. ‘What the opera critic of The Times actually wrote was that “the performance had all the gravitas of a Christmas episode of Coronation Street”.’

‘That’s harsh,’ I said.

I didn’t have any more tranquilliser, but the first-aid kit was still lying in the wings. One blow to the back of the head with the heavy case might be enough to put Lesley down. And then what?

Lesley cocked her head over to the other side – eyes still on me. ‘Oh look, boys,’ she said to the principal cast. ‘It’s the opera critic for The Times.’

I considered telling them I didn’t even read The Times, but I didn’t think they’d listen. I ran for the nearest fire exit on the basis that, by definition, it would be the shortest route out and, by law, always unlocked. Also the emergency exit signs were on a different circuit, and thus the only source of light.