In 1940 almost a year after the outbreak of the Second World War Allied radio operators at an interception station in South London began picking up messages in a strange new code. Using science maths innovation & improvisation Bletchley Park codebreakers worked furiously to invent a machine to decipher what turned out to be the secrets of Nazi high comm&. It was called Colossus. What these codebreakers didn't realize was that they had fashioned the world's first true computer. When the war ended this incredible invention was dismantled & hidden away for almost 50 years. Paul Gannon has pieced together the tremendous story of what is now recognized as the greatest secret of Bletchley Park.