Trade of Queens

A dissident faction of the Clan, the alternate universe group of families that has traded covertly with our world for a century or more, have carried nuclear devices between the worlds and exploded them in Washington, DC, killing the President of the United States. Now they will exterminate the rest of the Clan and keep Miriam alive only long enough to bear her child, the heir to the throne of their land in the Gruinmarkt world.
The worst and deepest secret is now revealed: behind the horrifying plot is a faction of the US government itself, preparing for a political takeover in the aftermath of disaster. There is no safe place for Miriam and her Clan except, perhaps, in the third alternate world, New Britain--which has just had a revolution and a nuclear incident of its own.
Charles Stross's Merchant Princes series reaches a spectacular climax in this sixth volume. Praised by Nobel laureate Paul Krugman as "great fun," this is state of the art, cutting edge SF grown out of a fantastic premise.