He went over to a table in the corner and spent a few moments locating a blank piece of paper. He noted down some names and addresses, the scratching of his pen the only sound in the room. On the edge of the table Sarah noticed the manuscript she had seen on her previous visit.

‘There have been others, no doubt,’ Dr Fowler said as he handed the scrap of paper to her, ‘but these are the ones that come most readily to mind.’

‘Thank you,’ she said. She pointed to the manuscript. ‘I see you have been turning your hand to prose. Are you writing a novel?’

Dr Fowler grabbed the pile of paper and held it to his chest, clutching it to himself as though afraid she might try to take it from him.

‘Have you been looking at this? How much have you read?’ he said, suddenly hostile.

Sarah hurriedly apologised. ‘I didn’t mean to pry. I merely caught a glimpse of it the last time I was here.’

Dr Fowler looked sheepish, as though aware that he had over-reacted.

‘What a poor host I am,’ he said, conspicuously changing the subject. ‘Do forgive me. I must get you some refreshment.’

Without waiting for a reply, he bustled out of the room, taking his manuscript with him, and returned with a glass of cordial which he insisted that she drink. Sarah took a tentative sip.

‘I would drink it all if I was you,’ he said. ‘You will be grateful for it later if you intend to visit all the houses on that list. Uninvited guests are seldom offered tea. This is Edinburgh, after all.’

She did not understand this last remark: she was never done serving tea at No. 52, whether guests had been specifically invited or not.

Dr Fowler seemed to sense her confusion and smiled.

‘That was a little joke,’ he said. ‘Though one born of a weary doctor’s experience making house calls in this city. I am from Glasgow originally. Hospitality is a little more forthcoming there.’

He seemed to be more amenable now that his manuscript had been safely stowed somewhere. Perhaps he is starved of company, she thought. She saw this as an opportunity to ask more about Mary Dempster, but she knew she would have to tread carefully. She dared not share her suspicions with this man who had recommended the nurse to so many patients.

‘I believe Mary Dempster is from Glasgow,’ she said.

‘I deduced as much from her accent. She told me a little about her upbringing, the tremendous obstacles that she has had to overcome. She and her sister were orphans. Her sister ended up in the asylum after becoming a prostitute, which is a testament to how it might have gone for poor Mary had she not been adopted. It is most impressive, I think, her choice of occupation, her compassion for others.’