The series follows a group of real-life volunteers as they are trained by former spies in espionage techniques, including maintaining a false identity, surveillance, persuasion and recruitment.
The programme's psychological challenges, dramatic tension, high production values, and personable cast led to its being called 'the most addictive thing on TV at the moment' by The Daily Telegraph.
SPY: A Handbook, a companion book written by Harry Ferguson, a trainer featured on the show, was published in 2004 by Bloomsbury in the UK (ISBN 0-7475-7523-1).
As the show progressed, recruits who failed to demonstrate sufficient potential as agents were unceremoniously dismissed from the competition.
In the final episode, Nicola Jackson emerged as the winner, but there was no prize other than the satisfaction of knowing that they had what it takes to be a real spy.