The Debatable Land was an independent territory which used to exist between Scotland and England. It is the oldest detectable territorial division in Great Britain. At the height of its notoriety, it was the bloodiest region in the country, and preoccupied the monarchs and parliaments of England, Scotland and France. After most of its population was slaughtered or deported, it became the last part of Great Britain to be conquered and brought under the control of a state. Today, it has vanished from the map and no one knows exactly where and what it was.

When Graham Robb moved to a lonely house on the very edge of England, he discovered that the river which almost surrounded his new home had once marked the Debatable Land’s southern boundary. Under the powerful spell of curiosity, Robb began a journey – on foot, by bicycle and into the past – that would uncover lost towns and roads, shed new light on the Dark Age, reveal the truth about this maligned patch of land, and lead to more than one discovery of major historical significance.