The film reveals the secret story behind one of the greatest intellectual feats of World War II, a feat that gave birth to the digital age.
In 1943 Bill Tutte, a 24-year-old maths student and a GPO engineer called Tommy Flowers combined to hack into Hitler's personal super code machine - not Enigma but an even tougher system, which he called his 'secrets writer'. Their break turned the Battle of Kursk, powered the D-day landings and orchestrated the end of the conflict in Europe. But it was also to be used during the Cold War - which meant both men's achievements were hushed up and never officially recognised.