She directed him to the privy, a small, dimly lit closet at the back of the house. As he relieved himself, he thought again about the bright and spacious bedroom he had just seen: at the front of the house, south-facing and enjoying a view had it not been fog-bound. Although it was Martha who had inherited money from her parents, it appeared Mary had the master bedroom. He considered what that implied with regard to who held the whip-hand in the house.

When he returned to the drawing room, Martha had already brought in a handsome tea service on a tray and was beginning to pour.

‘Have you spoken to Mary since last I visited?’ he asked.

‘Yes. She did come back, albeit briefly. She came to retrieve clean clothes and left again within the day. I gave her your card, though I assume from your visit that she has not made a point of speaking with you.’

As she said this, Raven realised that leaving the card had been a mistake. Once again, his judgment had been skewed by chasing the wrong cause. Martha would have told Mary that her visitors were investigating the deaths of three of her most recent patients. As a result, she most certainly wasn’t going to get in touch. More likely she had run to ground.

‘I have not had contact with her, no.’

‘And how goes your quest to identify this new affliction? Are there further sufferers?’

‘Four more, I believe.’

‘I was worried for Mary after we spoke, though I was not sure what to be looking for. She seemed well enough, physically, though she was irritable. She was far from forthcoming when I asked about the symptoms exhibited by her recently deceased patients.’

Raven got the impression this had been a fraught exchange. It also confirmed that Mary knew what he and Sarah were looking into.

‘I stressed that there was no implication that her competence or methods were being questioned, but she seemed angry nonetheless.’

‘Did she happen to mention the name of the family she is working for now?’

Martha’s expression became meek, the look of one not enjoying being made to revisit a memory.

‘I did enquire, but she scolded me for asking too many questions. “What business is it of anyone but mine who I work for?” she said. She was …’ Martha shook her head. ‘Mary can be rather short-tempered and aloof, but this was different. You said that this new illness made the sufferers delirious. Would that include being so defensive and suspicious towards the honest enquiries of her own stepsister?’

‘No, no, I am sure she is quite well,’ Raven assured her, though everything Martha said confirmed that there was something far wrong with Mary Dempster: just not the affliction that had claimed her victims.

‘How is your relationship with Mary generally, if you don’t mind my asking?’