This (the fourth) is far and away the best (so far) of Charles Stross' "Merchant Princes" series. In contrast with the last volume, where she was rather tied down, Miriam is now a free(er) agent again, albeit on the run from the Clan, the New Britain "Polis" and the spooky "Family Trade Organisation". The Clan is fighting both the FTO and the would be King of Gruinmarkt, the medieval parallel world - and losing. And a democratic opposition in New Britain begins to stir.
Overall, the story rattles along, with new elements dropped in - a fourth world, and hints of where the Clan's abilities come from - and some moments of comedy - as when the Clan's troops go to war dressed as medieval reenactors - then it stops, right in the middle of a battle. I'm already impatient for the next volume.
One mystery I've spotted this time - though it's not new - someone is taping the Clan's discussions. Clearly not the FTO, and New Britian doesn't have the technology - so who?