‘Could be that it reinforces anger that’s already there?’ I asked. ‘Or acts as a catalyst? It wouldn’t be an easy thing to prove scientifically.’

Nightingale smiled.

‘What is it?’ I asked.

‘You remind me of a wizard I used to know called David Mellenby,’ said Nightingale. ‘He had the same obsession.’

‘What happened to him?’ I asked. ‘And did he leave any notes?’

‘I’m afraid he died in the war,’ said Nightingale. ‘He never did get a chance to do half the experiments he wanted to. He had this theory about how the genii locorum works that would have appealed to you.’

‘What was his theory?’ I asked.

‘I believe I will make telling you that contingent on you mastering your next forma,’ he said. ‘I did notice that there were discrepancies between the script and Mr Punch’s actions. I’m thinking of Pretty Polly.’

As laid down in the Tragical Comedy, after killing his wife and kid Mr Punch sings a happy little song about the benefits of wife-murdering and, that done, he presses his suit with Pretty Polly. She’s a character who says nothing but ‘seems nothing loath’ when our cheerful little serial killer starts kissing her.

‘We don’t know he’s following that particular script,’ I said.

‘True,’ said Nightingale. ‘Piccini was relating an oral tradition, and those are almost never reliable.’

According to the possibly unreliable Piccini, the next victim was due to be a blind beggar who coughs in Mr Punch’s face and is thrown off the stage for his presumption. The script didn’t specify if he survived the experience or not. ‘If our revenant Pulcinella is following form,’ I said, ‘then the most likely target is going to be a tinny for the RNIB.’

‘What’s a tinny?’

‘A person with a collecting tin,’ I said, miming a shake. ‘People put their spare change in it.’

‘A blind man begging for money,’ he said. ‘It would be more useful to know who the revenant was and where he’s buried.’

‘Presumably if we know who he is then we can deal with his issues and lay him to rest peacefully,’ I said.

‘Or,’ said Nightingale, ‘we dig up his bones and grind them into dust, mix them with rock salt and then scatter them out at sea.’

‘Would that work?’

‘Victor Bartholomew says that’s the way to do it,’ Nightingale shrugged. ‘He wrote the book on dealing with ghosts and revenants – literally.’

‘I think we may be overlooking a blindingly obvious source of information,’ I said.

‘Really?’

‘Nicholas Wallpenny,’ I said. ‘All the attacks have originated near the Actors’ Church, which I’m guessing means that our revenant is located nearby. Nicholas might know him – for all we know, they hang out.’