I wanted this book to fulfill its early promise, but it didn't. My first real clue that it was going to be a dud occurred when I realized I was more than halfway through the book and we still weren't on the way to the supposed buried pyramid. There was a lot of grumbling by the young American woman about the strictures put on women (by their clothing, men's attitudes, etc.) that were acting to keep her from joining the rest of the expedition members on an equal footing. This could have been pared down considerably - we got the point after the first couple of mentions. Likewise, the shady nature of the expedition's likely competitors was almost immediately obvious to everyone except Uncle Neville - we didn't need to keep being beaten over the head with it -- and Neville's own behavior waffled between being a sharp customer to being completely muddle-headed - not at all consistent.
Another review stated something along the lines of "it was a good book through around pg. 380" and since the book only has fewer than 500 pgs. I couldn't quite imagine how that could be the case, but it was fairly accurate - right around that point the story utterly jumped the shark. I haven't actually finished the book at this point, but I'll likely zip thru the last 50 pgs. or so. If there are great mysteries yet to be revealed I'll be astonished. A very disappointing read.