The first part of this book takes a very simple universe with just three particles, making a triangle. Barbour shows how a configuration of such a universe can be represented as a point in a hypothetical space, Platonia. This leads on to discussions of absolute space and time. The book then introduces the reader to quantum mechanics and relatvity and so is suitable for the non-specialist reader. The book concludes with a discussion of Barbour's claim that the flow of time is an illusion, that all that we truly experience are instants. Barbour is a skilled writer, and I think that anyone interested in the philosophy of time will find much of interest in this book.
I have to say that I think that there are problems with Barbour's ideas though. Firstly relativity says that there are many ways of matching 'now' here with 'now' elsewhere. Barbour includes all such ways as part of Platonia, which I feel is excessively bloated as a result - mathematical fictions have been substituted for reality. The second problem is the deciding what exactly an instant is - do we have to accept uncountably many instants in the smallest interval. I find any philosophy which requires a particular structure for time at the lowest level to suspect. However, I wouldn't say that these were criticisms of the book, rather an indication of how Barbour's ideas can stimulate discussion.