‘As well as the papers on the suction tractor, galvanism and hospital fever. Not to mention the professor’s voluminous correspondence,’ Quinton added. Still the severe face; not even a hint of a smile. ‘I have left some papers on your desk that require your signature,’ he stated. ‘I bid you good evening.’

‘He is a graduate of Oxford University,’ Simpson said as the dining-room door closed, as though this explained everything.

‘What is a suction tractor?’ Raven asked.

‘Something that I have devised as a substitute for forceps in tedious labour, a rubber cup attached by suction to the infant’s head.’

‘Mrs Quinton has kindly agreed to take one of our babies,’ Mrs Simpson added, deftly changing the subject.

Raven wondered what she meant. He thought about the Simpsons’ children – David, Wattie, James and Jessie, who had been born just before he left on his travels – and wondered which one Mrs Simpson was planning to give away; trying and failing not to form a preference. Surely not the infant, he thought. Mrs Simpson noticed his confusion.

‘From time to time it is necessary to find foster homes for babies; orphans and those who cannot be looked after by their own parents.’

‘Yes, of course,’ Raven said, thinking she had described the matter with admirable delicacy. The unwanted, inconvenient progeny of upper-class indiscretion would perhaps be a more accurate description. He had not appreciated that the Simpsons were involved in such a project.

His thoughts returned to an odd sight he had once witnessed, despite the efforts of Simpson’s coachman to conceal it. The professor had visited a house on Doune Terrace, where through the window Raven saw him embrace a woman and then delightedly hug her child, an infant dressed in pink. The sight had troubled Raven ever since, unavoidably speculating as to Simpson’s role. Now, however, there appeared to be an alternative explanation, one that could account for the coachman’s discretion.

It might be a mystery solved, though it was not the prime question Raven sought an answer to. He desperately wanted to ask about Sarah but remained unsure how to broach the subject. He opted for an oblique approach and decided to enquire about the professor’s former assistants first.

‘I imagine that Mr Quinton is an extremely useful addition to the household,’ he said. ‘Of course, there have been a number of changes since I left on my travels. I believe Dr Keith has set up a practice of his own.’

‘Indeed. With his brother Thomas, who was once my apprentice, like yourself. They have premises on Great Stuart Street.’

‘And Dr Matthews Duncan?’

If there had been a thermometer in the room, Raven was convinced it would have indicated a sudden drop in temperature. He noticed an involuntary stiffening on the part of Mrs Simpson, her eyes darting towards her husband. He frowned before replying.

‘He too has set up his own practice.’