‘I have no regrets over employing a nurse, and certainly not this nurse. She was a caring and diligent woman, and she was with my wife to the last. She, in fact, is the one you ought to speak to. She will remember more clearly because I did not see a patient. I only saw Dorothy.’

‘What was the nurse’s name?’

‘Mary Dempster.’

‘Do you have her address?’

Dr Johnstone turned briefly to the sideboard as though it might be written down.

‘Actually, no. I advertised for help in the newspaper. There were two respondents and I chose her because she came with excellent references and had worked on the surgical wards of the Royal Infirmary.’

Dr Johnstone finished off his whisky and seemed far away once again. His subsequent words told Raven where his thoughts had taken him, and it couldn’t have been a pleasant journey.

‘What I can say is that the amount of blood Dorothy lost never made me uneasy. Considerably more was lost when Syme performed a similar procedure two years ago. Nor was there significant bleeding when Simpson removed the lint plug he had put in place at the time of surgery. The nurse will be able to corroborate that.

‘Dorothy seemed to be recovering after the operation, but then deteriorated over the coming days. I am not convinced this ailment was entirely related to the surgery, though perhaps that hindered her strength to fight it off. She was tormented: delirious, grasping at phantoms, her breathing shallow. It was as though she had fever, but her temperature was not elevated. She was at times unrousable, as though narcotised, and yet her pupils were normal in size. An odd combination. I do not think that I have seen it before.’

Raven felt something course through him as he realised that he had, only a few days ago. Dr Johnstone was describing the same symptoms George Porteous exhibited before he died.

He recalled Greta Porteous’s fear that she might develop the same disease, because their mother had died shortly before George fell ill. He had missed it at the time, but he now understood that her mother’s symptoms must have been similar for Greta to be so concerned.

Raven had previously thought that had Dr Simpson been present at the Porteous house, he would have known what to do. Now it appeared Simpson had been confronted with the same symptoms here and been equally confounded.

As Raven was shown to the door and bade his farewell, he had to suppress his excitement. He had deduced that in their eagerness to go after their enemy, these supposedly great medical men had missed the true significance here. There appeared to be a new, previously undiagnosed disease at large: one that spread rapidly and killed within days. It potentially represented a danger as large as cholera or typhoid. And no one had laid claim to its discovery.