On Friday 1st September 1939 - Germany invades Poland. By Sunday Britain has declared war. We explore the dramatic events that took place in the three days that changed Britain - and the world - forever. It's the countdown to war, told through the eyes of the British army and government as they prepare and mobilise; and ordinary Brits as their lives are swept up in the war to end all wars. Two presenters track the events of these three crucial days. They'll visit the places where key events took place and meet historians who fill in the details and show them documents and archives that bring the heightened emotions of this period to life.