Its book 3 in the series. Each one is a stand-alone story, but builds on the previous. I'd recommend starting with the first book.
James Asher is a Victorian secret agent and linguistic specialist, who has retired from field work to be a University don. His wife is doctor, and a researcher. (Rare for a Victorian woman.)
The vampires are very much people, and people of their own periods, as well as being vampires.
The first book - Those Who Hunt the Night /Immortal Blood (came out under two titles can't remember if it was a re-print thing or a UK/US variant) - something is killing the vampires of London and they can't work out what. So "hire" James Asher. In late Victorian London and elsewhere in UK.
There is a lovely scene where James Asher is fascinated to hear Elizabethan English being spoken by an Elizabethan era vampire.
Book 2 is largely set in Vienna, Constantinople and Paris.
Still waiting to get my hands on Blood Maidens - ordered, waiting for it to come.