Gaynor nodded. “Happened all the time. Let’s fast-forward to a hundred years after Rocque’s map.” She clicked a few more buttons and overlaid another map, this one with irregular shaded shapes throughout. “This is an ordinance survey map from the late nineteenth century,” she explained, “and the shaded areas represent structures, so we can easily see what buildings were in place.”

Gaynor paused a few moments, scanning the screen. “Okay, so this whole area was definitely pretty built-up by the mid-1800s. What this tells us is that even though Back Alley existed in the eighteenth century, it had essentially disappeared by the nineteenth century. But—” She paused and pointed to the screen of the ordinance survey map. “There’s a little jagged line here that seems to separate a couple of buildings, and it follows the path of Back Alley almost perfectly. Maybe even in the nineteenth century, Back Alley still existed as a walkway between the buildings. It’s just impossible to know.”

I nodded my head; despite my limited understanding of surveys and ordinances, I followed her logic. And with each passing moment, I felt myself more convinced that the narrow, jagged line representing Back Alley on the nineteenth-century map was related to the door I saw earlier today. The precise location of the door, relative to the two old maps that Gaynor had shown me, was simply too coincidental.

For the first time since finding the vial, I allowed myself to dream that I’d begun to unravel a significant historical mystery. What if something lay behind the door, something related to the hospital note, the vial, the apothecary? And what if I revealed the connection to Gaynor, and she thought it worthy of sharing more broadly with historians? Perhaps I’d be invited to assist with other research projects, or do a brief stint at the British Library...

I took a deep breath, reminding myself to follow the facts in slow, logical order. I couldn’t get ahead of myself.

“It’s pretty cool,” Gaynor continued, “cross-referencing all these maps. But if you’re looking to learn more about the apothecary, I’m not sure what these maps could tell you.”

I couldn’t disagree with her. “Okay,” I said, ready to move on to my second request—which was perhaps the more important one. “So, if we want to verify that this apothecary actually existed, what would be the best way to do that? Like I said, my own online searches were pretty fruitless.”