It is an astonishing story. A melting pot of Oxbridge dons (including Alan Turing, the father of the modern computer), maverick oddballs and more regular citizens worked night and day at Station X, as Bletchley Park was known, to derive intelligence information from German coded messages. Bear in mind that an Enigma machine had a possible 159 million million million different settings and the magnitude of the challenge becomes apparent. That they succeeded, despite military scepticism, supplying information that led to the sinking of the Bismarck, Montgomery's victory in North Africa and the D-Day landings, is testament to an indomitable spirit that wrenched British intelligence into the modern age, replacing false beards and dodgy accents with a technological precision that was to be fundamental as the Second World War segued into the Cold War.

Michael Smith constructs his absorbing narrative around the reminiscences of those who worked and played at Bletchley Park, and their stories add a very human colour to what was a highly cerebral activity, remote as it was from the blood and loss of the battlefield, but with such direct bearing. The code breakers of Station X did not win the war but they undoubtedly shortened it, and the potential lives saved on both sides stand as their greatest achievement. --David Vincent