In June, 1944, the Allied Forces stand on the brink of the greatest invasion of history: D-Day and the landing on the beaches of Normandy, France-the first step in the campaign to free Europe from the tyranny of Nazi Germany. But even as close to one million Allied soldiers are secretly assembled on the south coast of England preparing to invade Nazi-occupied Europe, Great Britain's iconic Prime Minister Winston Churchill (Brian Cox) struggles with the decision to embark on the operation. Fearful of repeating, on his disastrous command, the mass slaughter of more than 500,000 soldiers during World War I's Battle of Gallipoli in 1915, he is terrified that if the D-Day landings fail, he will be remembered as the architect of the war's greatest carnage. As D-Day approaches, Churchill-exhausted by years of war, plagued by depression and obsessed with fulfilling historical greatness-finds himself at odds with his fellow Allied military leaders-turned-political opponents: U.S. General Dwight D. Eisenhower (John Slattery) and British Field Marshal Bernard Law Montgomery (Julian Wadham). Meeting with Churchill in the days preceding the planned invasion, the two grow increasingly frustrated by the fearful and fatigued Churchill's reluctance to invade and attempts to stop the operation. It is only with the intervention of King George VI that Churchill agrees to move forward with the invasion, with the two discussing the possibility of observing the D-Day landings aboard an operational cruiser. It is Churchill's brilliant and unflappable wife Clementine Churchill (Miranda Richardson) who keeps him strong during those dark and possibly dire days. By injecting into her husband ever more confidence, courage and conviction-and acting as both an emotional blanket and a personal sounding board-“Clemmie” halts the exceedingly unwell Winston's physical and mental collapse, inspiring him to become a true hero of his age and Britain's most celebrated leader.