Excellent book. While the focus is on MI5 (Britian's domestic equivalent of the FBI) and MI6 (Britain's international equivalent of the CIA), Thomas shows, along the way, how all the global intelligence agencies are intertwined and opens a vivid window of insight into how they work together, apart, and often against each other.
Thomas brings the global intelligence community - and their bumbling and astounding ignorance, at times - under the microscope and into the hot, glaring white light of scrutiny in this sweeping history of spying.
He also provides compelling evidence that all these spook agencies chose to ignore, despite strong and persistent warnings, especially from one MI6 agent who realized (because he decided on his own to make himself an expert on the movement after Khomeni's takeover of Iran in the late 1970's), years before the idea of Muslim fundamentalism was on anybody's radar, that the radical calls for a wholesale jihad that a young Saudi (Osama Bin Laden) fighting in the war between Afghanistan and Russia in the 1980's was preaching had the potential to have dramatic global implications and consequences.
Thomas' book also provides a detailed look into the lead-up to the U.S. terrorist attacks on 9/11/01 (warnings within the US and global governments were everywhere beginning in August of 2001 and everyone knew it was coming, but no one did anything), the attack itself, and the aftermath, including the debacle of the 2003 war with Iraq (which was about personal vengeance by George W. Bush to finish what his dad didn't do -kill Saddam Hussein - and not about WMDs, which didn't exist at all at that time in Iraq), which only served to further destabilize the Middle East.
Embedded in this history of intelligence and the Middle East are things that will surprise you and possibly make the hair on your neck stand up if you're paying attention to who's involved and what they're doing.
This is a sweeping and big-picture history from which I am quite certain, because we breathe for a living, which seems to make us not only ignorant, at times, but also forgetful and dismissive of the past, these agencies and the governments they operate for will not gain wisdom and understanding from, nor will ensure are not repeated.