What if there was no USA? What if North America was four or five nations with the English speakers the minority? If the Spanish Armada had not been destroyed in that storm, Ivan the Terrible might well have married Good Queen Bess and established the Anglorussian Empire. WWI would be between the Japanese, the Anglorus, the Brazilians, and the Empire de Espana.
Percy Raleigh, a failed history professor and scribbler of speculative fiction is send on a fool's errand to London, Angloterre just as the First World War breaks out between the Empire of Nippon, The Ottomans, Brasil Negro and the Anglorus Empire, ARE.
The efforts of Nahezhda, "Hope," the ad hoc technological organization that was the last hope of the ARE have produced a respite for the Empire. Percy Raleigh is sent back to the North Colombian continent to set up aeroplane production in his home town of Elizavetgrad, what would have been San Francisco in our universe.
He has to traverse the wilds of the continent, finds that all the nations of North Colombia are aero-crazy, all want his knowledge, his aeroplane plans. His traveling companions, Gregori Rasputin and Lev Termen have other agendas.
Termen, in particular, believes he has established contact across a flaw in the aether with another civilization, and pursues this obsession to the point of insanity. Percy is kidnapped, loses his wife, gains a most difficult new one, and fights many battles, all in a desperate desire to be left alone.
Finally, Termen proves himself not quite so mad, and things become even more interesting. And scary.