PO Box 500, London W2; the nondescript address from behind which one of the worlds most famous Secret Services hid: MI5. This book, based on previously secret sources, lifts the lid on Britains Security Service.

The authors look in detail at MI5s role in the post-Cold War world; in particular, they consider its changing role as it took on the main responsibility in countering terrorist threats to Britain. Controversy has never been far away during MI5s battle against the IRA, which included sending deep penetration agents into the heart of Northern Irelands terrorist organisations. And in the twenty-first century, MI5 has had to face the deadliest terrorist threat of all from Al Qaeda. The book looks at MI5s attempts to prevent mass murder on the streets of Britain, including the failure to stop the 7/7 bombings in London in 2005.