Four
notorious Soviet agents operating in
Britain throughout
World War II and part of the
cold war. They were:
Anthony Blunt,
Guy Burgess,
Donald Maclean, and
Kim Philby. All four were
upper class gentlemen, and they met at
Trinity College at
Cambridge, where they were schooled.
Their effectiveness as double agents was propped up by their breeding and lifestyles, and all four went undiscovered for decades, doing serious damage to the British intelligence community from within.
The four were eventually brought down by an unwitting agent provocateur in MI5. In 1951, suspicion was cast upon Maclean, and an order was dispatched to have him arrested and interrogated. Learning of the order in advance from friends in the service, Blunt warned Philby, who in turn warned both Burgess and Maclean. When Burgess and Maclean fled the country, officials in MI5 realized that they must have been warned in advance by an accomplice.
A search for a "third man" began, and eventually led to Philby. From Philby, the connection to Blunt, the "fourth man" was drawn. The process of tracking the two accomplices down took roughly twelve years - mostly due to the fact that officers of the law were loathe to consider such distinguished men as potential enemies of the state.
The unmasking of the Cambridge Four arguably brought about the end of British class-exclusivity in intelligence circles, allowing for reform in recruitment techniques.