Halfway in, very enjoyable so far.
Finished. Made me want to read more about the French Revolution, the last Dauphin, and also some of the articles about music Donnelly referenced in her bibliography. You do have to swallow some rather big coincidences and accept a certain amount of mystery, but if you just go with it, it's an entertaining story.
Note to Megan: I don't know if it's just because you have been remarking recently about sentence fragments, but I found myself noticing them constantly through this book. I think it probably is just a way to make the first-person narrative voice seem less formal and more authentic and natural? But, yeah...non-stop.