Bishop: Betrayal: Chess Quest, Book 4 (Unabridged‪)‬

A strange and terrifying change has come over the Corridor of Keys now that it is under new management. The Grey Knight has taken over, creating a third faction in the game powerful enough to take on both Paladin and Nemesis alike. 

Now Rich must join forces with his former foes, undertaking a dangerous mission into the heart of the maze with his family that will determine the future of all knights, and then the entire world. But can he trust those who until recently wanted to see him in checkmate?