Hugh Sebag-Montefiore makes the observation that you need a unique angle on the Station X story as there are so many books now available on the subject. His take focuses not so much on Bletchley Park itself as the story in the field - or rather, at sea - with the captures of Enigma machines and code tables, but he also has an interesting back-story as his family owned Bletchley Park before it was sold to the government in the 1930s.
The book is obviously well researched, and starts with the story of Hans Thilo Schmidt, who sold some Enigma technology to the French in the early 1930s (even before the Nazis came to power), who passed it on to the British and the Poles. It's also interesting to see Dönitz having regular suspicions about the security of the Enigma system, but always ultimately put off by reports of its impregnability. Surely if anyone had joined the dots the way Sebag-Montefiore does, it would have been obvious that the Enigma had been compromised, though of course the evidence is only clear in this condensed form, after the fog of war has cleared and after patient trawling through archives.
The book's weakness is in its appendices, in which the author tries to explain some of the techniques used in breaking the code. Unfortunately I didn't find these intelligible at all, and whilst the author clearly felt obliged to try to describe some of the technical details, I think he would have been better sticking to his main story.