_The Merchants' War_ is the exciting and fast-paced fourth volume in Charles Stross' outstanding Merchant Princes series. I really enjoyed it a lot, as many ideas that were introduced and developed in the first three volumes really come to fruition in this book.
This installment finds the Clan in dire straights. They are essentially fighting a war on two fronts. In Niejwein Prince Egon, now King Egon, is waging a bloody and brutal war against the Clan and its supporters. With promises of great wealth and prestige (along with occasional threats of an untimely end if they refuse) many of the nobles are now aligning against the Clan. Though the Clan has powerful weapons and the advantage of world walking (they can for instance jump to our world, get in a car or even a plane, and then jump back over to Gruinmarkt, giving them a considerable advantage in speed) they have the disadvantage of smaller numbers and fighting an opponent who is doing his utmost to negate any advantages that the Clan may have (striking at more than one target for instance, making it hard to for the Clan to marshal its forces and strike hard via world walking as well King Egon himself making it supremely difficult for him to be assassinated).
In the United States the Clan is now fighting the United States federal government (or at least, is running and hiding from it). Having already lost entire networks of safe houses and not a few couriers thanks to Matthias' treachery, the Clan has little idea that the American government is increasingly viewing them as a bigger and bigger threat thanks to their rising fears over nuclear weapons that they may have planted in American cities. Correction, that were planted in American cities, as the Family Trade Organization discovers one(the Family Trade Organization is the top secret federal agency assigned the task of studying the Clan and ending it as a threat, the organization comprised of relocated members of the intelligence, defense, and law enforcement communities, including Mike Fleming from the DEA, former boyfriend of Miriam).
The Family Trade Organization is not content though with just playing defense on American soil; slowly but surely, first by use of captured couriers, they have put a few agents on Niejwein soil, hoping to gather intelligence, make a few friends, and even run some operations of their own. Mike even makes contact with some members of the Clan (who of course want to use this back door connection with the American government for their own ends). Foremost among the contacts that the FTO would like to make is with Miriam Beckstein, whom the FTO knows now is a world walker.
The Clan would also like her back. Problem is no one quite knows where she is, as when she escaped Prince Egon's attack on his father and brother, she fled as best she could. The only knot she had to use to enable her to world walk lead her to New Britain, where she arrived shaken up, without money, in a bad part of town, believing that she would be imprisoned or even if killed if she ever set foot in Gruinmarkt again, throwing herself on the mercy of her dubious revolutionary allies in New Britain, "friends" of Erasmus Burgeson. Are they really friends or are they just using her? Is she just exchanging one set of enemies for another? Even if they are friends, is it a conflict she can prevail in, given that they want to fight the oppressive royal government of New Britain?
Wait there's more! The series takes on a decidedly science fiction feel as two programs are initiated. The United States launches a secret, high-tech effort to understand the physics of world walking, hoping they could create a machine or at least by pass the Clan as a way to get to "fairyland," while the Clan launches a much lower budget but ultimately incredibly important program to see if they can make their way to still other worlds besides the three that they know about.
Very exciting, it ends with a tremendous cliffhanger.