The Tree of Heaven by May Sinclair

After Drayton's death Frances and Anthony were sobered and had ceased to feed on illusions. The Battle of the Marne was fought in vain for them. They did not believe that it had saved Paris.

Then came the fall of Antwerp and the Great Retreat. There was no more Belgium. The fall of Paris and the taking of Calais were only a question of time, of perhaps a very little time. Then there would be no more France. They were face to face with the further possibility of there being no more England.