An interesting idea, unfortunately its potential is not fully realized by this book.
A young woman comes out of the barbarian wastes. At first she is assumed to be mentally deficient - but it soon becomes clear that she is several orders of magnitude more intelligent than anyone around her - and ruthless enough to use that intelligence to her own ends.
The material here was originally published as several separate stories featuring the character of Tatja Grimm. Unfortunately, they don't really come together as a novel. Although they work as separate stories, as a novel they're missing essential pieces of background information and other narrative elements to achieve coherency. The story brings up interesting concepts and questions, but barely explores them, leaving a reader with the impression of a tale which wants to rise above the level of a simple sci-fantasy adventure, but doesn't, quite. It's too bad, because there are many tantalizing elements here. I especially love the concept of the traveling publishing company that purveys science fiction and fantasy stories on an alien world. I really do like Vinge's writing in general - but 'A Fire Upon the Deep' this is not.