In April 1953, George Blake returned to Britain as a national hero, one of a small group of British diplomats who returned alive from three hard years as a prisoner in North Korea. What the government, the press and public didn't know, though, was that during his time as a prisoner he had become a communist and decided to work for the KGB. Director George Carey goes deep in his investigation of what is considered to be one of the world's most renowned treacheries.