I'm surprised at those reviews that say there is "a hint of" or "some" romance in Bk 3 of the Wrexford/Sloane series. It seemed to me there was quite a lot of romance in this, which detracted from the rather Gothic mystery. I still don't especially like how the romance is being handled, either. It's much less smooth than C. S. Harris' St. Cyr series or Kate Ross' Julian Kestrel books.
Of the three W/S books I found this the least satisfying. I'm never fond of the cliche of a villain afflicted with insanity, and throwing in the Frankenstein element was IMHO a definite plot weakness. I realized it's an authentic part of scientific history but I'm tired of it, nonetheless, so found it more irritating than mysterious.
More facts are revealed about Charlotte's background, and that's the other false note. She's nobility, not a commoner at all. How convenient for the romance to continue! Wouldn't want Wrexford (eventually, we assume) marrying beneath himself.
I do like the side characters - the Weasels, the maid, the surgeon, the valet (altho he has less to do here) - so for the near future, I'm willing to buy the next couple of W/S books that come out. After that, we'll see how it goes.....