The Fall of the Cabal. Someone introduced me to this series a few weeks ago. I thought it was mind-expanding, thought-provoking and very well done! I highly recommend it!
And when you are through you will want to continue with The Sequel to the Fall of the Cabal. Janet Ossebaard has not yet published all of these but is trying to get one out every week of so. There are 10 in the series of 17 available as of this post.