What is the strange formation on the Atlantic sea-bed? Could this be the fabled Atlantis? Is it an ancient Orbiane city, flooded after the end of the last ice-age? Following Mary and Si's previous experience,they investigate discoveries from the mid-Atlantic to Egypt.There they find more questions; Did the Egyptians build the Giza pyramids? How did they carve and move the massive stones? Their discoveries challenge our accepted view of human pre-history. But they are not the only ones interested in these discoveries. While searching for the truth, they have to ensure that these discoveries don't fall into the wrong hands.