Sarn Helen - Helen's Causeway - is the old Roman Road that runs from the south of Wales to the north. As Tom walks the route, sometimes alone, sometimes in company, he describes the changing landscape around him and explores the political, cultural and mythical history of this country that has been so divided, by language and by geography. Running alongside this journey is the story of Tom's engagement with the issue of the climate crisis and its likely impact on the Welsh coastline.