Accordingly the book is divided into three parts:
Part 1 is readable (and understandable) by anyone with a nodding acquaintance with the basic language of cosmology: events, lights paths, galaxies, black holes and so on. It covers the whole story of the book in a way as untechnical as possible given the scope of the topics covered.
Part 2 covers the same ground again but with enough technical details to satisfy a reader with basic knowledge of mathematics and/or physics.
Part 3 consists of appendices which are referred to in the other parts and which also contain the highly technical material omitted from Section 2.