This one was a change of pace from the other books I've read in the Clockwork Century series. First, it follows just one character (versus 2). Second, it moves at a slower pace and is less non-stop action than the first books in the series. Third, the steampunk gadgetry seemed more on the periphery this go-round, perhaps because Mercy is mostly an observer through a lot of the book (an active observer, yes, but she really doesn't have any hands-on experience with the war machines). None of these is a deal-breaker; I still got hooked by the story and liked the characters. It was just different from what I expected. 
 This book picks up on the east coast in a Confederate Hospital. The war has been going on for 20 years. Vinita, "Mercy", Lynch, an experienced nurse, has just learned that her Yankee husband has died, and then hears that her estranged father has been gravely hurt in Washington state. Feeling adrift and also perhaps hoping to get a break from the constant fighting, she starts the long journey west. Of course, this means that her trip will be anything but boring. 
 We have travel by airship, boat and train, and sporadic fighting as the Union or Rebel forces advance/retreat as the case may be. You get a glimpse at the steam and diesel-powered war machines (walkers, massive train engines, etc), but since Mercy is a passenger there isn't a lot of up-close steampunk gadgetry. There is zombie action, too, of course, and the final third of the book is action-packed. 
 There is a lot more history in this one, and since you follow just one character (versus bouncing back and forth between 2 POVs), you get a lot more time to linger over events and people. 
 Priest does tough-as-nails characters really well, and there is no shortage of them here. I expect to see some of these characters in later books. A few characters from previous books make an appearance here as well. 
 It can be a risk, changing the main characters in each book, but I feel Priest does an excellent job of keeping the spirit of the series intact. I will be eagerly awaiting book 4.