Spring, 1941. The Second World War has entered a dangerous phase, withBritish ships being torpedoed in the Atlantic and nightly bombing raids on majorports. At Bletchley Park, top secret home of the nation's code-breakers, therace is on to crack the German Enigma code and thus prevent further naval andmilitary losses. This endeavour is suddenly very close to home for FrederickRowlands, blind veteran of the Great War, when his daughter, Margaret, whoworks at 'the Park' as a cryptographer, is arrested on suspicion of betrayingsecrets to the enemy.Then a young woman is found murdered, and Rowlands is drawn into a deadlybattle of wits where he must decode a series of clues that will lead him to thekiller and enable him to discover the real traitor at Bletchley Park.