The Squire's Tale by Margaret Frazer is an absolutely delightful medieval who-done-it with the starring investigator of Dame Frevisse. She's a nun and like other people in fiction serials who are good at solving crimes also appears to find herself in the midst of them time after time. As my husband says occasionally when we watch other who-done-it shows on television, "They ought to lock her up."
At the end I cried. It was also a love story and, for me, the mark of a "good" book is that I cry at the end.
As time goes by I expect to see more reviews for this author. You can read more about Margaret Frazer on Wikipedia.