Walking the Downs on the Sussex-Hampshire border, Robert Macfarlane explores the poet Edward Thomas's love-affair with paths and tracks. For twenty years, Thomas walked what he called 'the long white roads' and 'frail tracks' of England's chalk country. Then in 1916, he enlisted and was sent as an officer to the chalk landscape of Arras in Northern France, with its far more dangerous paths, 'Where any turn may lead to Heaven / Or any corner may hide Hell'. He was killed on Easter Monday, 1917. Producer Tim Dee.