The spy is as old as history but spy services are quite new. Britain founded the first, Her Majesty's Secret Intelligence Service, in dubious circumstances in 1909. Others followed until no country considered itself a nation unless it had a corps of spies. The biggest and most expensive is America's Central Intelligence Agency, the CIA, formed as recently as 1947. The CIA's principle enemy was the Soviet Union's KGB, and the clash of these two giants has been the thrilling stuff of history, novels, films and plays. In assessing the real role of the spy, Phillip Knightley brilliantly takes all the real characters of the spies themselves - Mata Hari, Sidney Reilly, Richard Sorge, Kim Philby, George Blake, James Jesus Angleton, Ruth Kuczinsky, the Rosenbergs - and answers the crucial question. Did they make any difference to the course of history? Or was spying the biggest confidence trick of our time?