XPD by Len Deighton

June 11, 1940 – where is Winston Churchill?

A private aircraft takes off from a small town in central France, while Adolf Hitler, the would-be conqueror of Europe, prepares for a clandestine meeting near the Belgian border.
For more than forty years the events of this day have been Britain’s most closely guarded secret. Anyone who learns of them must die - with their file stamped:

XPD - expedient demise