Paris, 1940: Walking through Montmartre that morning was like the eerie calm right before a storm. The roads were deserted. We carried on, arm in arm, and then finally, we saw them. Columns and columns of soldiers, spreading through the streets like a toxic grey vapour. 'You must write about this, ' he whispered to me. 'You must write about the day freedom left Paris.' As Nazi troops occupy the City of Lights, American journalist...