What is the theme in Sir Thursday by Garth Nix?

Trusting one's own abilities is another theme in the book. Arthur, Leaf, Suzy and Fred are all young adolescents who are thrust into a world in which they are at a disadvantage. Arthur and Leaf must learn about the world of the House while trying to save their own lives and the lives of others. Suzy and Fred are Piper's children who have been "cleaned" and don't remember large parts of their lives. They are also people who come from a lower class in the House.