Here's the Amazon listing, but the Harper Collins page has a much longer summary:
The first installment in Neal Stephenson’s Bomb Light cycle, Polostan follows the early life of the enigmatic Dawn Rae Bjornberg. Born in the American West to a clan of cowboy anarchists, Dawn is raised in Leningrad after the Russian Revolution by her Russian father, a party line Leninist who re-christens her Aurora. She spends her early years in Russia but then grows up as a teenager in Montana, before being drawn into gunrunning and revolution in the streets of Washington, D.C., during the depths of the Great Depression. When a surprising revelation about her past puts her in the crosshairs of U.S. authorities, Dawn returns to Russia, where she is groomed as a spy by the organization that later becomes the KGB.
Set against the turbulent decades of the early twentieth century, Polostan is an inventive, richly detailed, and deeply entertaining historical epic, and the start of a captivating new series from Neal Stephenson.
Incidentally, he also has a new interview at the Atlantic, honestly a pretty lackluster one--basically, he's not impressed with AI so far, and assumes much more interesting applications will be discovered. The base inspiration for the primer in Diamond Age was his child's mobile--you were supposed to snap on more sophisticated shapes as the child aged.