At Yonaguni, Hancock scuba dives 70 feet beneath the waves to an astonishing submerged step-pyramid structure, never seen before on British television. It has the appearance of a great work of architecture but if it is man-made then it is the oldest-known monument on earth. Science proves that the last time the land it stands on was above water was 10,000 years ago. Hancock dives again off the Micronesian Island of Pohnpei, near the spectacular megalithic city of Nan Madol, to explore further mysterious underwater ruin. Many of the monuments that Hancock takes us to, notably the temples of Angkor in Cambodia, and the Pyramids and the Sphinx in Egypt, were carefully and accurately laid out on the grounds as images, or 'copies' of particular constellations of the stars in the sky. Thus the Pyramids copy the belt of Orion, the Sphinx copies the constellation of Leo, and the Angkor temples are laid out in the pattern of the stars in the constellation of Draco.

Graham Hancock's global quest looks at astronomical, cultural and symbolic evidence that, while scattered around the world, links inextricably together. He starts in Peru, where the Nazca lines, the biggest drawings in the world, etched in the desert over 2000 years ago, are, he believes, just one of a series of global ground maps of the night sky, part of a world wide grid that is the legacy of an earlier civilisation that left clues to its identity throughout the world. At the pyramids at Giza, in Egypt, he shows how the famous King's Chamber's shafts are exactly targeted at the stars in the belt of Orion as they would have been in the skies at the date of 10,500 BC. How did the Nazcans possess the understanding to know how to plot that progress with a retrospective knowledge of the constellation's movement? But as well as astronomy and mathematics, Hancock draws on other evidence. History tells us that Egyptians never crossed the Atlantic. How then, to explain, the culture of pyramid building in central and South America. Possibly a coincidence. How then, to explain the recurrence of one symbol - that of a feathered serpent - in Cambodia, Egypt, Central America and South America? Coincidence? And how then to explain the mystery of the massive caved heads left behind by the mysterious Olmec civilisation in south America.

Graham Hancock is on Easter Island, where the mysterious statues of carved heads have perplexed scientists for hundreds of years. Why did the inhabitants of a remote, tiny, Pacific island carve and place such elaborate statues? Last year, Graham received reports of a mysterious structure off the tiny Japanese island of Yonaguni that had been submerged since the sea-levels rose over 10,000 years ago. The programme follows his expedition, staffed by respected authorities in the fields of geology and Egyptology who explore the structure, the height of a six story building, the size of the Great Pyramid and in astonishing footage, follow trenches, angles and planes that form a pattern that logic states cannot be an accident of nature. There may be many explanations for the similarities and connections Hancock has found in his decade of exploration but he believes that the best explanation is, "A lost civilisation, lost in the night of time, that once touched them all [the sites]. I think it's possible that that civilisation knew something we do not and its survivors after the last great cataclysm that brought the last Ice Age to an end went to extraordinary lengths to keep that knowledge alive".