Even though this is an old topic, I just saw it for the first time and would like to comment.
I haven't seen the mini-series but I have read the book and it's excellent. Kate Mosse is one of my favourite writers. She is an English author who lives half the year in Carcassonne. She specialises in writing books about the stories and legends of the Languedoc set in two different time periods (with related plots).
Labyrinth is the first and most famous of these books and is of the most interest to us as Carcassonne game fans because one of the time periods is medieval (1209) and part of that story is set in the cité of Carcassonne. The other two books in this series are Sepulchre (where the historic time period focus is the late 19th century or early 20th century - I don't remember exactly) and Citadel (where the historical focus is on WWII). These last two books are set in the same region but don't focus on the medieval city of Carcassonne like Labyrinth does. They are still excellent though, as is a a smaller book she wrote called the Winter Ghosts which, while not part of the above series, is still set in the Languedoc.