This was kind of disappointing, but not because it's a bad book. Jonathan Kirsch seems to have written this with a low expectation of his audience's reading skills. Perhaps it's because he spends part of his time writing stories for NPR, but I found his chapters to be written as separate essays rather than as parts of a cohesive book. Certain facts and stories tend to be repeated over and over again, as if we haven't already read them. It was much like watching a modern TV show that shows recaps after every commercial break.
The chapters chronologically cover the major movements of the Catholic inquisition from it's origins in the 12th century to the recent and final official gasps in the 19th. Telling the history in this way allows our author to show the development of authoritarian technique throughout the centuries, rather than presenting the Spanish Inquisition, say, as a lone aberration.
And this is the book's theme, that these techniques developed by the church (torture, the use of informants, guilt by blood relation) still reverberate today in Western culture. He spends the last few chapters examining the Nazi and Stalinistic purges and methods of promoting fear, as well as our own “war on terror.”
Strangely, the book is a response to “apologists” for the Inquisition as well as to people who would generally support torture and the reduction of rights. It's one of those cases where you don't really need to make the argument. And I doubt that anyone who thinks that water-boarding is a valid method of information gathering, or who looks at the massive torture and murder of huge swaths of people in the name of control and can excuse it in the name of historical context, is going to be swayed by argument, anyway.
And so, this is a light history book written for an audience that already agrees with it's point of view. There also isn't a lot of first-person research, outside of references to the actual Inquisitor's Manuals which we can all now read in various archives online. Most of the writing is actually a survey of other books written on the subject, and sometimes resorts to quotations of yet other books from those.
If you're never going to read another book on the subject, this will give you a good, quick overview. It's an easy read; you'll have a fresh water-cooler discussion topic after a few days. But, if like myself, you want something with a bit more “meat” to it, I'd recommend going with something listed in the bibliography, perhaps starting with Marion Starkey's The Devil in Massachusetts and then moving on from there.