OK plot, well written, good worldbuilding, BUT: The female characters were handled so badly that it was noticable and annoying. I've read lots of books describing societies where women have less power than men, so that's not the problem. But the women were mostly invisible, or when they appeared they were described so briefly that you could practically hear the author muttering "Let's get boring this female stuff out of the way so I can return to important things". Minor spoiler: 
 (view spoiler)[Durendal's love is described as deep and important, but only in passing -- two sentences about how much he and Kate loves each other, and then it's back to the important stuff with the king. No hint of conflict of interest between family life and service to the king, no use of the obvious plot possibilities related to Kate's occupation as a sniffer (someone who can detect magic). (hide spoiler)] 
 I expect this kind of treatment of women from Dickens, but not from someone living today.