Steven Harper's The Havoc Machine is the fourth in the "Clockwork Empire" series. However, it sits somewhat apart from the events of the other books, and the opening notes specifically recommend it for new readers who haven't read the other installments. I did find that it stood quite well on its own.
The details of the clockwork plague are captivating: one plague that creates a minor zombie menace, and a much greater two-sided boon/menace in the form of the clockworkers. They create astounding devices that can give their countries great power, but they also lose such touch with their humanity that they become dangerous to those around them. Thad, who hunts and kills clockworkers, is an interesting point of view character as the novel explores the idea of what it means to be a clockworker, and what it means to be an automaton.
Some of the 'secrets' in the story are telegraphed too much, making it difficult to understand why the characters don't pick up on them. Also, I found the tone of the book somewhat discordant: most of the tale is dark and gritty fantasy/steampunk, but the nature of the clockworkers occasionally veers into the silly end of comic-book mad scientist villain territory. Also some of the tsar's choices and decisions felt too convenient to the plot.
The question of free will in the context of automatons arises, but it seems to be handled a little inconsistently. Supposedly certain conditions have to be met before an automaton develops 'sentience' as such (sorry for the vagueness, but I'm trying not to give away plot points), but there are minor automaton characters (such as Dante the parrot) that seem to exhibit such traits without the relevant criteria having been met.
There are some lovely plot twists and ideas in here, and a very nice exploration of the nature of clockworkers as well as the nature of their automatons. There is some minor dark material to be aware of (things occasionally get a bit bloody)--I say this simply so you can decide whether it's a book that suits your tastes. The concept of clockworkers is brilliant, and I love how it's handled. All in all this isn't the best steampunk novel I've read (so far that honor goes to A.A. Aguirre's Bronze Gods), but it's certainly an interesting read.
[NOTE: review book provided by publisher]