In a nutshell: This is a real-life murder mystery from the 1800's. Not as good as the over-the-top reviews make it out to be, but still worth it for the first and third "acts" (about 100 pages each). The middle 100 pages draaaags. It drags because the history itself drags as the investigation gets bogged down and stalls, but still, I didn't need to feel the frustration of the bogging-down process myself!
A surprising guest appearance in the third act from Thomas Huxley (Darwin's bulldog). It doesn't give anything away to say this, but the old saying is true: The author suspects "the scientist did it." (Not Huxley but the person he knew!) I don't know that I agree ... a scientist's output is so vast (and the conflicts in a scientist's life happen so frequently!) that you can glean quotes here and there that could lead to anything. However, I have to say her theory probably makes the most sense of anything, given the facts in this case. I'm left with reasonable doubt.
So, as a real mystery with real implications in which you can "play along," there's really not many other books like this one. Just don't feel bad skimming the middle 100 pages.