Mary Gentle’s Ash is a really big book. It’s probably pushing half a million words. It is also very good.
The most useful way to describe it is “historical fantasy”, although it’s probably technically science fiction. But if you think you’re going to read a historical fantasy, you’ll have a pretty good idea of the sort of book you’re going to get, while “science fiction” would be very misleading. The eponymous Ash is a female mercenary captain in Burgundy in the late fifteenth century. Naturally, she is involved in a number of wars, and she gradually gets caught up in bigger and bigger events.
The rest of this article will discuss specific plot elements of the book, and thus probably spoil things for you if you haven’t already read it.