You know how when you read a series of books the plots begin to run together ... not with Ellis Peters. Although I recommend reading each of the books in the Brother Cadfael series in order, this is my favorite.
In many ways the plot is actually quite trite, female widow needs husband who's not interested in her money. But the way Peters puts her elements together is unique to her and our hero. Her stories are just a way to convey her love of history, not only the factual information but also the mood and atmosphere. It is the latter part that she does so well.