He was thirsty, and, after his long walk through the fog, in need of something warming. But another reason he readily accepted was that it would keep Martha busy in the kitchen while he took a look around. This time he was determined to be mindful of evidence that Mary was in fact present: two used teacups, for instance, or two place settings at the table.

As soon as Martha left the room, Raven put his hands upon the two chairs by the fire to test whether they might both be warm from having been recently occupied. Only one was but that did not surprise him. He suspected he would find no such clues today, as Martha seemed altogether less anxious. If Sarah’s notion was correct, then on this occasion her sister truly was not at home.

Nonetheless, he crept out into the hall on light feet and gently pushed open the door opposite leading into the room where Sarah thought she had spied movement at the window. It was a spacious and brightly decorated bedchamber, its sturdy double bed seeming likely to have belonged to the late Mr and Mrs Dempster. The bed was neatly made, and thus there was no way to determine whether it had or had not been slept in the previous night. He lifted the counterpane. The sheets were tucked under the mattress with military precision and he recognised the handiwork of someone trained at the Royal Infirmary.

There was a plain gown laid out on the bed, a clean apron placed on top of it. The gown was dark blue with white braiding on the cuffs. He thought it similar to the one he had seen Mary wearing at the Porteous house, though he could not be certain as he had seen her only briefly on that occasion.

There was a row of books upon the window ledge. Raven’s eye was caught by the spine of one that he thought might be a copy of Christison’s Treatise on Poisons, though he could not read the lettering clearly from where he stood. He was about to step closer when he heard a voice at his back.

‘What are you doing in Mary’s bedroom?’

Raven jumped.

‘My sincere apologies, Miss Dempster. I was in search of the water closet.’

He noted that she seemed almost as alarmed at her discovery as Raven had felt at being discovered. He thought of Sarah’s contention that she was afraid of her sister and could barely believe he had failed to see it before.