Edward VIII still reigns following the suspicious death of his mistress, Wallis Simpson. France has fallen with 300,000 men of the British Expeditionary Force taken prisoner trapped on the beaches of Dunkirk. Left with almost no troops, guns or tanks, Britain stands alone against the might of a German Wehrmacht armed with assault rifles, main battle tanks, aircraft carriers and a pair of 'superguns' firing seven tonne shells across the English Channel.
Day after day, Squadron Leader Alec Trumbull and a fast-dwindling number of broken veterans and inexperienced new-recruits take to the skies against the seemingly endless streams of German aircraft. His Spitfire damaged in the heat of battle and pursued by enemy fighters he can't outrun, Trumbull is saved at the last moment by a strange jet aircraft that can land and take off vertically.
He discovered that the advanced aircraft belongs to the Hindsight Unit: a UN task force from the 21st Century sent to combat a group of Neo-Nazis also returned from the future to aid Nazi Germany wins the Second World War. As technology accelerates and events begin to spiral out of control, Trumbull finds himself drawn into Hindsight's desperate struggle to prevent a seemingly inevitable invasion of Great Britain and return history to its true course.