Joan Clarke - The biography of a Bletchley Park enigma

The life of Joan Clarke, who worked alongside Alan Turing at Bletchley Park during World War 2 and subsequently at GCHQ. Having been recruited by GC&CS at the beginning of the war, Joan stayed with what then became GCHQ until well past retirement age. She worked on the unmasking of Philby, Burgess and Maclean during the Cold War.