Going back to the discussion about whether the book is "dark" - I would say that, yes it is very dark. A young man whose world and just about everything he knew, has been literally wiped out. The grieving process that he goes through, the burying of the dead, the wish that he had died along with his world is incredibly dark. Terry deliberately takes everything away from him - everything except the person he is deep inside. The darkness is such that it says that sometimes everything must be destroyed if it is to be rebuilt and rebuilt better - with new ideas. Mau discovers his past and that discovery also destroys a part of him. It destroys his faith in the gods, but reveals the power of humanity. This is just the darkness of Mau's journey. Just about all of the other characters also go through a destruction of their beliefs and a reawakening. They find who they are and not who other people tell them to be.
The main female character also goes through a huge change due to having her personal world destroyed. She changes her name from Ermintrude to Daphne, a move that is a part of her breaking away from her pampered privileged life. Unlike Mau, it seems she wasn't particularly religious. She had a scientific mind that she had not really been allowed to improve. In the Nation she has to use her scientific mind, but also learn to be human. The bizarre scenes where she is trying to hang on to her class structure is excellent because, like Mau's religion, she had clung to it until she realised just how useless it was to her.