‘You are a nurse too?’ Raven asked. Once again, he could have moderated his tone to perhaps sound less incredulous.

‘Yes. It was not the life I envisaged for myself, but I had to find a purpose after everything that happened.’

She looked away briefly, as though her thoughts had gone elsewhere.

‘You have a fine house,’ Sarah said. If Raven was going to express his surprise at the incongruity between her job and her surroundings, she reasoned she ought to balance things by complimenting the latter.

‘Thank you. Mary and I moved here after my parents died. I was fortunate enough to inherit some money. We could not hope to rent such a place on a nurse’s earnings, though certainly private nursing is far better paid than in the hospitals.’

Sarah wondered at her reference to ‘my parents’, rather than ‘our’.

‘I encountered your sister briefly at the Porteous house,’ Raven said. ‘I might be mistaken, but by her accent I took her to be from Glasgow. And yet you sound—’

‘Edinburgh born and bred,’ Martha interrupted with a proud smile. ‘I ought to clarify: Mary came to us when I was thirteen and she was twelve. She was in an orphanage in Glasgow.’

‘She is your adopted sister,’ Raven stated.

‘Yes. Though it amused us down the years how often people would say we had a resemblance while they thought we were true sisters. Introduce an idea into someone’s head and they will soon start to paint a picture around it.’

How true, Sarah reflected, her mind inevitably turning to poor Miss Grindlay, Mrs Simpson’s sister, who had paid a high price for painting just such a picture.

Quiet settled upon the room, and with it the awkwardness among people with nothing left to say to each other. It prompted Raven to get to his feet. He produced a card and handed it to Martha.

‘I would be obliged if you would ask your sister to contact me at her earliest convenience when you do see her. It is particularly imperative that she speak to me should she or any of her patients exhibit similar symptoms to those of George Porteous.’

‘Of course, Dr Raven.’

As Sarah stood, her eye was caught once again by the plants in the garden, particularly the one she was unable to name.

‘I see that you have some medicinal plants in the garden, but there is one I cannot identify, to the right of the rosemary.’

Martha had a look through the window, her expression strained.

‘Mary is the one who has a passion for horticulture. Having grown up in a Glasgow slum, the very notion of a garden has always held great appeal. I think the plant you are referring to is potatoes.’