Hancock has really written a great book here. It is perhaps his most honest work to date in as much as he is prepared to look at things that may not fit his theory and is prepared to say when he's wrong. His theory that ancient kingdoms were flooded at the end of the last ice-age is a sound one. It has been neither proven nor disproven. However, rather than let it remain a theory, Hancock has actually gone out this time to look for himself and he makes a pursuasive argument. Underworld is much more academic than his previous works but he still has a large mountain to climb in being taken seriously. The truth of the matter is that well respected archaeologists are already investigating some major deep sea discoveries and Hancock is in reality collecting this data into a coherent volume. His theory however pertains to the entire globe, whereas these respected scientists tend to see their discoveries on merely a local scale. Unlike his previous books where Hancock makes a far fetched theory/assumption and bases his argument for the entire subsequent book on that questionable assumption, this time Hancock has been more analytical and has crafted a cogent argument that develops solidly, rather than being built like a house of cards. I bought Underworld and Stel Pavlou's brilliant Atlantis novel, Decipher at the same time. Both are excellent. Both contain masses of research. Which one is fact and which one is fiction? Well that's the fun of reading them side by side.