The Special Branch of the Metropolitan Police was originally formed to combat a campaign of Irish republican terrorism, but soon took on wider responsibility for the monitoring of anarchists, Bolsheviks and suffragettes. This book presents a complete history of the service until its 2006 merger with the Anti-Terrorist Branch. Combining documentary sources with recollections from their own former colleagues in Special Branch, the authors trace its distinguished history and describe many acts of bravery and high-risk intelligence-gathering.