The Curiosity Keeper by Sarah E. Ladd

Camille Iverness helps her father who is a collector and dealer of curiosities by tending the shop and keeping the accounts. Their shop is in the poor part of London, but Camille has learned to take care of herself. Jonathan Gilchrist is the heir to an estate in Surrey, but the future of his family's wealth is in jeopardy because a large uncut ruby has been stollen from his father's collection. When Jonathan goes to Camille's shop in search of the gem, he instead finds and rescues Camille from ruffians who are also after the ruby. Even though Jonathan is a gentleman, and Camille is a shop girl, their mutual attraction grows as they try to find out what has happened, to the gem but can they really trust each other with a family fortune at stake?

This is a pretty good historical mystery romance.  Camille is both capable and vulnerable, and Jonathan is noble and selfless. The book is more romance than mystery.  There isn't really an investigation and clues like in a detective novel, and there isn't a particularly clever resolution to the mystery. Still, the question of what happened to the gem provides a nice framework for the development of the relationship. I did struggle a little with this book when one of the main characters made a particularly dumb decision.  I hate when the main character is stupid, but in this case, it wasn't to bad, and I was able to finish to book.  There are more in this "series" but they are unconnected stories that just share the same time and setting, so it is not important to read them in order. I may read the next one, eventually. (2015, 341 p.)