I realised suddenly that Nightingale was looking for reassurance, which I found extremely worrying. ‘Just make sure you stay ahead of me,’ I said. ‘How do we find the Magistrate?’

Nightingale smiled. ‘We just need to get his attention,’ he said. He turned and addressed the empty centre of the room. ‘Captain Nightingale to see the Colonel.’

The smell of old sweat and spilled drink grew stronger, and a figure appeared in front of us. This ghost seemed more transparent than my old friend Wall-penny, thinner and more ghostly, but his eyes glittered as they turned on us. Sir John Fielding had worn a black bandage to hide his blind eyes, and Nightingale had called on the ‘Colonel’, so my guess that this was Colonel Sir Thomas de Veil – a man so routinely corrupt that he managed to shock eighteenth-century London society, generally considered by historians to be the most corrupt in the history of the British Isles.

‘What do you want, Captain?’ asked De Veil. His voice was thin and distant, and around him I could sense rather than see the faint outlines of furniture: a desk, a chair, a bookcase. Legend had it that De Veil had a special private closet where he conducted ‘judicial examinations’ of female witnesses and suspects.

‘I’m looking for a warrant,’ said Nightingale.

‘On the usual terms?’ asked De Veil.

‘Of course,’ said Nightingale. He drew a roll of heavy paper from his jacket pocket and proffered it to De Veil. The ghost reached out a transparent hand and plucked it from Nightingale’s fingers. For all that he did it casually, I was certain that the effort of moving a physical object must be costing De Veil something. The laws of thermodynamics were very clear on the subject – all debts must be paid in full.

‘And which miscreant are we looking to apprehend?’ asked De Veil, and placed the paper on the transparent desk.

‘Henry Pyke, Your Honour,’ said Nightingale. ‘Who goes by the name of Punch, and also by the name of Pulcinella.’

De Veil’s eyes glittered and his lips twitched. ‘Are we arresting puppets now, Captain?’

‘Let us say that we are arresting the puppet master, Your Worship,’ said Nightingale.

‘And the charge?’

‘Murder of his wife and child,’ said Nightingale.

De Veil tilted his head. ‘Was she a shrew?’ he asked.

‘I beg your pardon, Your Worship?’ said Nightingale.

‘Come now, Captain,’ said De Veil. ‘No man strikes his wife without provocation – was she a shrew?’

Nightingale hesitated.

‘A most terrible shrew,’ I said. ‘Begging Your Worship’s pardon. But the babe was an innocent.’