And what of that instinct? The thought of that troubled him as much as the guilt: what it said about his nature. What he feared he had inherited from his father.

You have the devil in you, his mother had often said, and though she spoke with humour and affection, he could not help but wonder if it was a way for her to express her own fears for what he had been born with.

Perhaps the hardest thing was that there was nobody he could talk to about it. Standing here now in the professor’s study, he donned a neutral expression and concealed his feelings.

‘My travelling companion decided to extend his stay in Berlin.’

‘A city I have yet to see. Chance would be a fine thing. Always so much to be done.’ The professor looked around for somewhere free of clutter to place his bag. He moved a pile of papers from his desk to a chair and seemed sad for a moment. ‘I hunger for a book and thirst for the time to read it,’ he said.

Raven had so much he wished to tell the professor. There were names to conjure with, institutions of vast renown, techniques and procedures that he was sure would fascinate his ever-curious mind, but there was to be no such opportunity, as almost immediately the doctor began discussing the details of the patient they were about to see. It was frustrating and yet oddly reassuring. This part, at least, was like coming home.

‘A widow of more than a year. Her husband was an army surgeon who succumbed to an infectious fever within days of their arrival in India, leaving the poor woman to make her own way home. She now looks as if she is in the advanced stages of pregnancy and, with the husband having been dead for longer than the period of a normal gestation, a certain amount of embarrassment has resulted from her condition. What do you think of that, Dr Raven?’

Raven felt a slight inward glow at being addressed by his hard-won title, but this quickly left him as he sought to make an intelligent reply to the professor’s query. He thought for a moment. Her apparent condition was bound to prove highly injurious to the widow’s good name, but her reputation might well prove the least of this woman’s worries.

‘She might actually be with child,’ he suggested. This answer directly questioned the woman’s virtue but there was no room for drawing-room decorum when discussing medical matters.

‘Sometimes the most straightforward explanation is the correct one,’ the professor agreed. ‘It may, of course, be a phantom pregnancy – I have encountered one before – but on that occasion the patient fervently believed she was carrying a child, whereas this lady insists that pregnancy is not a possibility, in spite of her appearance.’