I've been getting interested in Bletchley and the role of the codebreaking team after a visit to the D-day beaches recently. Tenuous link I know, but anway. This book is extremely well reserached and very detailed, very detailed. The explanations of how the ciphers were broken tested my maths knowledge, but I think I got it after re-reading some paragraphs a few times. I'm still only two thirds of the way through the book, but I would recommend it to those of you interested in the man Turing, his life, his family, personality and of course sexuality, which he had to hide during that time. The author obviously is an expert on turing's life and has his own website about Bletchley, Turing, historical documents and so on. Basically, Alan Turing and his team at Bletchley not only cracked the German messages, but layed down the work for the invention of the computer.