First off, this isn't a typical Amazon title, rather it is the product of PS Publishing, which puts out limited, signed editions by various science fiction and fantasy authors. Specifically, "Jigsaw Men" by Gary Greenwood was limited to 300 hardcover and another 500 paperback copies, and at the time of this writing, some copies were still available from the publisher. Moreover, there are copies available on the internet, and should the opportunity to acquire a copy present itself, I would strongly recommend doing so.
A big problem with many alternate histories is the need for exposition at the expense of plot. For example, an author spends so much time explaining why the South won the Civil War, precious little time is left for characters to interact and grow in the altered timeline. One would expect that this situation would be compounded in a novella, where length becomes a limiting factor, and then compounded again by the odd amalgam that forms the backbone of Gary Greenwood's "Jigsaw Men". It's hard enough to succinctly portray the above scenario, but Greenwood has gone far beyond that relatively simple scenario, as he posits the "what ifs?" of a world in which Dr. Frankenstein succeeded in making his monster and Martians invaded and were beaten off as predicted by H. G. Wells. Happily, Greenwood succeeds admirably; producing a world that is drastically altered, nicely realized and fully believable, and at the same time, introducing an engaging plot and characters, and all the while drawing relevant parallels to our own world.
If it wasn't for the setting, "Jigsaw Men" would be a noir-esque detective thriller. Loaded with all the elements of the genre (seedy locales, prurient scandals, streetwise cops) the mystery would be compelling enough without any allo-historical element. However, it is this altered timeline that really makes the story; it elevates what would be an entertaining, but generic, mystery into an interesting commentary on morals, and international relations. The British Empire of Greenwood's timeline is plainly a metaphor for the U.S. today, and in many ways his Prussia is today's UK. In "Jigsaw Men" Britain is still an Empire, and the globe's dominant power, with Prussia as a staunch, if somewhat restive ally. Furthermore, much like today, no matter how benevolent the UK attempts to be, there is an element of hubris which colors its actions. Thus, a relatively straightforward disappearance becomes a major espionage crisis as Greenwood questions whether cracks in hegemony must become holes, and whether or not that is a bad thing.
Now that I've spent so much time saying why Greenwood has produced something beyond a merely altered timeline, I feel obligated to state how much I loved the purely alternate history elements. The premise is engaging enough, but Greenwood takes it in directions I never would have expected. To delve too deeply might spoil the plot, but Frankenstein Monsters as the ultimate soldiers and Martian technology as the greatest State secret of Great Britain are just two of the interesting ideas put forward. However, it is the small things that make or break an alternate history, and Greenwood comes up with plenty to make his story feel familiar but foreign. Again, I don't want to give anything away, but my personal favorite was a sly reference to the passions of British soccer fans: he mentions fans of rival teams have friendly chats after games.
Like most things in literature (or life) there's no right or wrong way to write alternate history. However, truly great additions to the genre transcend the academic exercise of imagining another world (which is no mean accomplishment when done well) and reveal something fundamental about the human condition, or even more interestingly, our values and culture. To my mind, no one has done this better than J. N. Stroyar in her massive "The Children's War". Likewise, another PS Publishing title, Ken Macleod's "The Human Front", offered an intriguing critique of political systems, and was, like "Jigsaw Men" an unusual premise in a short form. Both of those books won the Sidewise Award for Alternate History; it is my expectation that "Jigsaw Men" will get a long, hard look for the award, and it would not surprise me in the least if it resulted in a trophy for Gary Greenwood and PS Publishing.