Unicorn's Blood

What is the Book of the Unicorn and why is Queen Elizabeth 1 searching for it so desperately? What ancient scandal threatens her throne as she fights to avoid executing Mary, Queen of Scots? And who is the man painfully waking up in a dungeon with no memory of who he is or how he got there?
Unable to trust anyone, the Queen must recruit where she can. David Becket and Simon Ames, two mismatched heroes, unwillingly find themselves in the thick of a dark and murderous game.