It is fascinating. People often disregard the book because its main thesis, the identity of a mole within MI5, appears to be misguided in light of post-Cold War knowledge. But there's more to the book than Wright's speculations -- it's his direct experiences with things like analyzing The Thing that make the book worth reading.

Also, in the same vein, I highly recommend R.V. Jones' 'Most Secret War' on his experience as Chief Boffin in the UK during WWII.

Chapter after chapter devoted to figuring out what the Germans were up to on the technology front, then one-upping them. Lots of engineering porn.

"The Ministry of Ungentlemanly Warfare: Churchill's Mavericks" by Giles Milton describes a lot of the equipment that SOE developed - e.g. the original limpet mine depending on condoms and boiled sweets and, of course, developed in someone's shed and tested at the local swimming pool.

Seconded. It really emphasises how far things have come in a relatively short time, with the technology not so long ago being very basic compared to what we read about from, for example, Snowden.

Also checkout the Billion Dollar Spy.