I was unfamiliar with the series before this installment and it works perfectly well as a standalone mystery. I will be picking up the others in the series.
I really engaged with Lady Frances from the beginning. She's intelligent and well spoken and able to take care of herself. She and her personal maid have a sort of Holmes and Watson dynamic (which Lady Frances refers to often). They're engaged by an elderly family acquaintance to find out what happened to the friend's daughter over 30 years ago. It's the coldest of cold cases and Lady Frances agrees to investigate while maintaining at least some social decorum.
The characters are easy to relate to and well written. The dialogue and narrative flow naturally and are enjoyable. It's a very light fun mystery and the fact that Lady Frances doesn't suffer any real social stigma from her very unconventional lifestyle or habits isn't a deal breaker.
It reminds me a bit of Carola Dunn's Daisy Dalrymple series or even Kerry Greenwood's wonderful Phryne Fisher books (but more chaste and cleaner :) I enjoy cozy period mysteries and even though Mr. Koreto's Edwardian London isn't slavishly drawn from real history, it's still easily recognizable as London.
The mystery itself is well written and the denouement is satisfying.
Four stars, well worth a look.
Disclosure: I received an ARC at no cost from the author/publisher