The Shattered Castle (The Ascendance Series, Book 5)

When King Jaron returned to Carthya he brought with him a device that supposedly shows the way to a great treasure, but now everything is going wrong: Castor, the son of an old enemy, is conspiring against him and wants the throne for himself, his fiancâee, Imogen, seems to have turned against him, and the Prozarian Monarch has invaded his kingdom and taken Jaron's castle--but Jaron has a lot of experience at hiding and escaping, and he is not willing to leave Carthya or Imogen in the hands of his enemies.