Although this book was nothing like what I imagined, I found it to be very interesting and engaging. I was a refreshing contrast to another book that I am reading in small spurts. I know that I am going counter to the average opinion, but I think this is worth at least a "3.5" if not a full "4.0".
Here we get to see the life of the first organized and effective detecive force. Although I knew that Pinkerton had been around for the Civil War, I did not know much about him or his organization. (Except, of course, that Dashiell Hammet worked for them for a couple of years and that they were involved in strikes.)
Although this is fiction, I assume that much of the broader strokes are taken from historical fact. If even half of the "missions" told here are true, then reading a histry of Pinkerton's would be quite enjoyable.
In this book we see how the organization was formed and the kind of people that were hired to be operatives. While there is techinical details on how they might assume disguises (or more deeply craft personae, the bulk of this book is character-driven. From Pinkerton's own point-of-view we get a look at his world, family, organization, and the "War of Rebellion". The bulk of the book covers the years 1860 thru 1865 during which Pinkerton worked with and for the Union.
Again, how factual all this is, I don't know right now, but the writing is crisp, fresh and the story moves briskly. Mr. Lerner has been a screenwriter, so the emphasis on character and human interactions is not surprising, but the book is fully-fleshed as well.
I offer one quote from page 144:
"She then retrieved her pearl-handled pistol. I watched, hypontized as she checked the action and inserted five bullets into the chambers.
Danties and a gun. Oh, she was irresistible!"
You'll have to read the preceeding paragraph to understand the "danties" reference, though.