When Captain Ridley's shooting partyA arrived at Bletchley Park in 1939 no-one would have guessed that by 1945 the guests would number nearly 10,000 and that collectively they would have contributed decisively to the Allied war effort. Their role? To decode the Enigma cypher used by the Germans for high-level communications. It is an astonishing story. A melting pot of Oxbridge dons 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, 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 their cerebral activity. The code breakers of Station X did not win the war but they undoubtedly shortened it, and the lives saved on both sides stand as their greatest achievement.