Discussed are the efforts to break the Enigma Code and the role played by the Colossus computer, designed by T.H. Flowers. In 1977 the Colossus was still on the secret list, so details are fairly sparse, but the programme benefits enormously from an interview with Tommy Flowers. There are also valuable contributions from others present at Bletchley Park during WW2 such as Gordon Welchman, Harry Golombek and Peter Calvocoressi.