What is the theme in The Egyptologist by Arthur Phillips?

Insanity is another theme in this book. Ralph goes insane while chasing after treasure that does not exist. He enters this state in stages, starting with too much belief in the existence of Atum-hadu. He only has unsupported documents that may be ancient fiction telling a mythical story about a heroic king. Ralph's quest for proof begins with a nearly sure chance of disappointment.