Described by Northern Ireland Prime Minister James Craig as the 'root of all evil', the Irish Boundary Commission that convened in 1924 was a symbol of hope for nationalist Ireland and fear for unionist Northern Ireland. Offered to Sinn Féin plenipotentiaries to help push the 1921 Anglo-Irish Treaty over the line, it was believed the Commission would transfer large tracts of the six counties back to the newly established Irish Free State. However, delayed by the Civil War, British political turmoil and unionist non-cooperation, and hampered from the start by the vague and ambiguous wording of the clause in the Treaty, by the Irish Free State government's naivety, by the intransigence of unionists, and by the duplicity of successive British governments, it ultimately bolstered the unionist cause, leaving the border unchanged. Swathes of Northern nationalists were abandoned to their fate, their trust in both the British and Free State governments irrevocably damaged. One hundred years on, Cormac Moore illuminates the fascinating and infuriating story behind the Boundary Commission's momentous failure, which would have long-lasting, catastrophic consequences for the entirety of the island of Ireland.