Dandy Gilver and the Proper Treatment of Bloodstains by Catriona McPherson - Lots of fun to read. Dandy is a great character and the mystery is good. This book also addresses the class divide between aristocrats and their servants. There is a wonderful moment when Dandy, posing as a lady's maid, is upon questioning tongue tied as to what her fictional first name is, as if it had never occurred to her that lady's maid would actually have a first name. This gives her cause to ponder what her own maid's first name might be. Sadly, this is the most recent Dandy Gilver book so I shall be waiting for the next volume and then waiting for the library to get a copy.
A Beautiful Blue Death by Charles Finch - also a period mystery (although somewhat earlier), also with aristocracy, servants and murder. Not as good as Dandy Gilver but thankfully the first in a series of four.