When Dr Simpson and Raven left the house, they carried with them several fat, satiated leeches and an abundance of toffee wrapped in paper. Almost as soon as they were ensconced in the carriage, Simpson unwrapped one of the paper parcels and offered Raven a piece.

‘Thank you, no,’ Raven said. ‘I have a painful tooth.’

‘You should have that attended to,’ Simpson suggested.

Raven was about to say that his work commitments left precious little time for such things but thought the better of it. He did not wish to seem disagreeable or lacking in gratitude, especially when the professor’s own workload appeared to be wearing him down.

‘Does it pain you now?’ Dr Simpson asked.

‘Yes,’ said Raven, putting his hand to his jaw. ‘It kept me awake for much of the night.’

Simpson stuck his head out of the carriage window and called for Angus, his coachman, to stop. He then gave the man directions that Raven could not hear. A few minutes later the carriage turned from the main road onto a side street lined with a small row of shops.

Raven looked out and saw that they had drawn up outside a druggists’.

‘Why have we stopped here?’

‘A small amount of chloroform on a piece of lint applied directly to your troublesome tooth will provide relief until you see a dentist,’ Simpson said, getting down from the carriage. ‘Unfortunately, I have none in my bag.’

Raven was about to object that there was no need, but the throbbing in his jaw said otherwise. He was bemused, however, by Simpson continuing to suggest chloroform for every ailment. If he persisted, he would begin to look like a snake-oil salesman brandishing a cure-all. If he ever proposed its use as a treatment for baldness Raven would be compelled to intervene.

Somewhere gloomy in the back of his mind, he thought about the bottle he had been forced to supply to Flint, and worried what the money-lender and his crew of reprobates planned to do with it. It did not lessen Raven’s guilt that he had been left with little choice but to acquiesce, though he did console himself with the truth of what he had told the man: chloroform would not do for them what they hoped it could – but that had not prevented misconceptions flooding the newspapers, and pharmacists regulating their supplies accordingly.

They entered the shop to find a small woman with grey hair vigorously scrubbing down the counter. Her shop was well-stocked and neatly kept, not so much as a jar out of alignment with its neighbour. The woman looked up at them and scowled, as though customers were a great inconvenience.

‘What can I do for you gentlemen?’ she asked, putting down her cloth and wiping her hands on her apron.

‘I would like to purchase a bottle of chloroform,’ Dr Simpson said, giving her his warmest smile.