Really quite excellent. I would have liked a little more explanation of the science behind it all for a perfect score, but overall I was both fascinated and impressed. I hesitate to call real people "characters", but McKay's decision to focus on a number of personalities was a good one - it really rounded out the professional narrative to read about the lives of the men and women involved in the Y Service, and how they reacted to and connected with the events going on around them. It made the whole book highly accessible.