His premise is that the fools and troubadors of the Middle Ages in Europe and the surrounding areas of the Mediterranean were in a very secret Guild, one to collect information on the ruling courts and to promote peace whenever possible. And when it is not possible, to pick out the most promising contender to any given throne, and to try to help him/her get that throne.
The first book is called Thirteenth Night, and is a sequel to Shakespeare's Twelth Night. It is told from the point of view from the Fool, who has to return to Orsino after many years to solve a mystery there.
Other books tell of the Third and Fourth Crusades, and one tells the real story behind Hamlet. 
