I read this book over the course of several days with many interruptions so through no fault of the author I find it difficult to think of the book as a coherent whole.
Kelly went into great detail about where the plague continues to live today. The strain that survives in marmots is particularly vicious and the danger was apparently well known by natives centuries ago.
The book is great for little snapshots of how different communities became infected by and responded to the plague. There are a number of quotes from primary sources. But at times it seemed repetitive, this is how x place was probably infected, the strain was probably pneumatic and later bubonic.
Interesting, but not the best book I've read on the subject, though I'm willing to concede that my divided attention may make my impression of the book unnecessarily harsh.