I found the story a bit clumsy in places but mostly good (that might be a little harsh; it gets 4.05 on Goodreads). The medieval setting is very gritty and thoroughly de-romanticised and largely set around the arrival of the Plague. The author is American and I thought she had a better understanding of medieval Britain than of 'modern' Britain! On the whole a pretty good book, though not exceptional. However it is an SFMasterworks book. Also there are three other books and one short (90 odd pages) all in the same setting that I've not read yet. I believe the second one - To Say Nothing of the Dog (Victorian I think) - is also in the SFMasterworks.