This was such a fun read. Gorgeous descriptions of the fashion and food of the time and a vivid depiction of life and politics in the 1700s. I guessed the South Sea Bubble would play an important part and I wasn't disappointed.
If I had any niggles, it was with Koen's habit of putting explanations in brackets after anything she thought the reader might not understand. I know what an apostle spoon is and a stomacher, and even if I didn't, I'd go and look it up. If you're that keen to explain everything, just use footnotes as they're less likely to snap me out of the story.
The book reminded me of Forever Amber, but with a heroine who I sympathised with, rather than one I wanted to strangle. (Though I did want to yell at her for not choosing the man who truly loved her).
And talking about Forever Amber, the descriptions of the plague in that book were brilliantly written and researched, and in Through a Glass Darkly, Koen does the same with smallpox and it is heartbreaking.
And there are plenty of loose ends to be tied up in the sequel.