The definitive puzzle book from the top-secret British intelligence organisation, GCHQ. The secrets of the country depend on you. Find out if you’ve got what it takes to be a code breaker? GCHQ’s top-secret codebreakers have always protected the country – from Bletchley Park’s war-ending WWII breakthroughs to saving us all from life-destroying foreign cyberattacks. But what kind of mind does it take to work there? And do you have the brain power, cunning and resourcefulness to pit your wits against them and win? Here, taken from their archives, are decades of codes, puzzles and challenges for everyone to try. You’ll discover: Tips on how to get into the mind-set of a codebreaker; Puzzles ranging in difficulty from easy to brain-bending; Challenges that have never been solved; and Insight into the organisation's top secret history dating back to 1919.