The Revolution Business: Book Five of the Merchant Princes

Things are going badly for the Clan in this SF novel of the Merchant Princes the immensely popular series by Charles Stross. Locked in a vicious civil war for control over the kingdom of Niejwein their army is bottled up inside a fortress under siege in two parallel universes at once. Duke Angbard the Clans leader has been laid low by a stroke: plotters are already conspiring in readiness for the deadly dance to come. Miriam rescued from a tight spot in New Britain finds the hopes of the young progressive faction focused on her. But do they want her as a leader or a figurehead? She soon finds herself thrown into a desperate struggle for power. Meanwhile unbeknownst to the Clan researchers working for the US government have achieved a technological breakthrough.