France 1940. The war is not going well and the Allies are in full retreat. The Belgians have been vanquished and the French fight rearguard action after rearguard action. Amongst this, the British have assembled the fleet of Little Ships to extract their exhausted army. Separated from his unit, one man heads for the coast to join the evacuation and get home. But it's a troubled road: on the way he picks up a downed RAF pilot and a lone soldier who's survived the massacre of his platoon. They reach Dunkirk a day late. Everyone has gone. All is lost...or is it? Who is The Lost Man? How did he get home? And why does Churchill want him as his personal agent?