This is the only Cadfael mystery I've ever had to restart because I just couldn't get into it the first time. I suspect the reasoning for that was that it was around the time I was reading about the Inquisition and there's really only so much religious intolerance I can handle. I didn't even make it to the murder the first time!
This time, I finished it and enjoyed every moment of it. Given the amount of so-called heresies abounding at the time (and, really, ever since such a thing was invented), I really don't think there was any way to avoid covering the topic in at least one of the Cadfael novels. I think she did it very well, personally.
On top of that, there's a murder, which may or may not be related. There's a love story, which is not uncommon, Cadfael has a weak spot for young love. There's also dissension amongst both monks and lay folk regarding what constitutes heresy as well as what constitutes an acceptable use of one's own wit, which may or may not be dependent on one's sex and station in life. And, there's plenty of information about the crafts of the time, in this case the creation of vellum, which was skin that was used as paper (for lack of a simpler way of explaining it). I'm really glad I went back and finished this one, it was definitely worth it!