This is fascinating, well written, and thoroughly researched. What the Author suggests is that many, if not all, of the passage grave sites in the UK are aligned to various astronomical features. Mainstream archaeology only looks for solar alignments, but James shows that many of these sites are linked to lunar phenomenon, as well as constellations. In particular he draws attention to the connections to the star Sirius.
He spends the first part of the book relating the alignments of the different sites, and showing how each is unique. In the second part of the book he discusses the artwork and it's connections to astronomical arrangements. The third part, he explores the theories of others who have preceded him in this work. Finally, in the last part, he explores his own connections and what they may mean.
This is a short, fairly easy read, although a bit dry at the start, it is interesting all the way through. Despite being an easy read, it is not a work of speculation, it is based on research and fact, and is presented as such. Only at the very end does Mr. Swagger allow himself to speculate a bit, and even that seems rather reserved. An enjoyable and recommended read.