Palaeontologist Dr Tori Herridge investigates the natural disaster that destroyed the massive chalk land-bridge that once connected Britain to continental Europe 450,000 years ago . Beginning her inquiries in Norfolk, she discovers what life was like before the ancient mega-flood, where she meets an amateur palaeontologist who uncovered the biggest mammoth skeleton ever found, and examines the 850,000-year-old footprints of an early human family perfectly preserved in prehistoric mud. She then travels to Kent and the white cliffs of Dover to detail how the mega-flood happened, joining an `oceanographic' expedition seeking to document evidence of this cataclysm found on the bed of the English Channel.