'Then he needs to be brought in for questioning.'

'That may be difficult, sir.'

'Why – Mr Voke told you where his son worked.'

'I called on the proprietor, Mr Solomon Stern. He didn't speak well of Stephen Voke. Apparently, his work was very satisfactory at first but he became lax. Also, his timekeeping was poor. He began to arrive late and leave early. What annoyed Mr Stern,' he remembered, 'was that a young lady was always loitering outside the shop in the evening. As soon as he saw her, Stephen Voke left.'

'Are you telling me that you never actually met Voke?'

'He no longer works in Hatton Garden.'

'Did his employer give him the sack?'

'Mr Stern never had the chance to do so,' replied Leeming. 'He has not seen hide nor hair of Stephen Voke for a week. The young man has terminated his employment there without warning.'

'Then you should have sought him at his lodgings.'

'I did, sir. I went to the address given to me by Mr Stern.'

'Was Stephen Voke there?'

'No, sir,' said Leeming, 'and he never has been. He gave a false address to his employer. Nobody seems to know where he is. Stephen Voke – and, presumably, the young lady – has vanished into thin air.'

Tegwyn Rees was a tall, angular, emaciated man who looked as if he should be lying on the slab beside the corpses he dissected. When he was introduced to Colbeck by Jeremiah Stockdale, he regarded the inspector through cold, almost colourless eyes.

'Why do we need detectives from London?' he said with undisguised resentment. 'The crime was committed on Welsh soil. I'm sure the superintendent could have solved it without interference.'

'I came to help, Dr Rees,' said Colbeck, 'and not to interfere. In any case, Superintendent Stockdale is very much involved in the investigation. His officers are making enquiries about the source of that sulphuric acid even as we speak.'