At 9am on 20 January 1607, a massive wave devastated the counties of the Bristol Channel. It came without warning, sweeping all before it. The flooding stretched inland as far as the Glastonbury Tor. Two hundred square miles of Somerset, Devon, Glamorganshire and Monmouthshire were inundated. Up to 2,000 people died. Yet for 400 years, the killer wave of 1607 has been forgotten. Timewatch relives the terror and the human tragedy of 1607 and follows the research of two scientists who are increasingly convinced that the wave was not simply a freak storm but a tsunami.