This is the introductory episode to the series and describes the Battle of Tannenberg that occurred in the opening months of the First World War.  With most of its army concentrated in France and Belgium, the German master plan for fighting a two front war called for only a small field army to delay and contain an anticipated Russian invasion of Prussia while the western allies were quickly defeated.  The stakes could not have been higher as the German high command watched with growing dread the appearance of two massive Russian armies on their eastern frontier only two weeks after Germany's declaration of war;  much sooner and in much greater numbers than had been expected.  This is the story of one of the most improbable and impressive military victories of all time that, had it gone the other way, would have resulted in the occupation of Berlin and defeat of imperial Germany at the beginning of a war that would devastate the continent.