Part one of this book covers the history of Buddhism in Siam (aka Thailand) as well as the history of the Thai throne, with particular focus on the thirteenth century or so onward. The second part of the book is an anthropological analysis of the place of the wat in contemporary Thai society (up to about 1971). He's not an exciting writer and there are a fair number of bad sentences in the book, but he does seem to be largely correct, partially because his thesis is incredibly complex. In fact it's so complex I can't really summarize it here, which is annoying.
If you are studying Thai Buddhism you will probably have to read this book as part of your prelims; if you are not studying Thai Buddhism you have no reason to read this book.