First of all, grateful thanks to Sarah Armand, Gemma Briggs and Iain Standen at Bletchley Park; the work that has gone into restoring the codebreaking centre, and the huts in which those world-changing miracles took place, continues to draw in many thousands of visitors. For information on the Park, its many attractions and its opening hours, visit www.bletchleypark.org.uk.
Even more grateful thanks to the geniuses Roy and Sue Preston, who devise devious puzzles and problems with such style, flair and ingenuity. Huge thanks are also due to Radiya Hafiza, hawk-eyed copy-editor Lindsay Davies and particularly Grace Paul for the enormous job of bringing the book together with such speed, care and calm; also to Phoebe Swinburn, for letting the world know about it. And to Sarah Emsley, whose idea the book was in the first place!