This book reads like some old role-playing books I used to enjoy. There was inevitably some section given over to describing the history of the fictional Earth; that section invariably consisted of a long list of dry facts that you quickly decided just to skim. The second half of Gray's book reads like that, but with less coherence or narrative and only slightly more references.
In fact, the role-playing analogy can be taken further. Go dig out some old Rifts books: many of them spell out an alternative Earth where all legends are based on fact, and magic has reawakened, revealing just how much the ancients knew and could do. Druid circles and ley lines and pyramids are all revealed to be forgotten lore, far superior to modern ingenuity.
This book claims exactly that, but it is not nearly so entertaining to read.
I genuinely tried to approach this with an open mind. Gray refers to some ancient artifacts that I would be interested to learn more about, but he gives no thorough descriptions or even references. What is more, these potential gems are buried in long lists of "evidence" that is clearly irrelevant. He seriously argues that ancient pictures of bird men prove that mankind could fly? Woe to the future archaeologists that discovers some dusty mirror of DeviantArt.
One mystery I have not tried to solve is when this book was actually written. The copyright is 2014, but I do not think there were any allusions to anything after the 1980s. At one point, he explicitly mocks modern man for failing to build the Channel Tunnel.
On a final note, Gray should be ashamed of his bait-and-switch approach to religious proselytizing.
my favorite quote: "In other words, evolution has an answer it likes, and is trying to make the questions, and the facts, fit its answer."