The Kingdom - Clive Cussler

The husband-and-wife team of Sam and Remi Fargo are used to hunting for treasure, but they aren't used to hunting for people - until an investigator friend of theirs goes missing, and they promise to search for him. What they find, however, will be beyond anything they could have imagined.

On a journey that will take them to Tibet, Nepal, China, Venice, and Siberia, the Fargos will find themselves embroiled with black market fossils, an ancient Tibetan kingdom, a lost landmass in the North Sea, stone-age ostrich egg shards inscribed in a cryptic language, a pair of battles separated by thousands of miles and hundreds of years...and a skeleton that could just turn the history of human evolution on its head.