The Woman of Mystery by Maurice LeBlanc

Toul, Bar-le-Duc, Vitry-le-Francois. The little towns sped past as the long train carried Paul and Bernard westwards into France. Other, numberless trains came before or after theirs, laden with troops and munitions of war. They reached the outskirts of Paris and turned north, passing through Beauvais, Amiens and Arras.

It was necessary that they should arrive there first, on the frontier, to join the heroic Belgians and to join them as high up as possible. Every mile of ground covered was so much territory snatched from the invader during the long immobilized war that was in preparation.