The Crown Jewels was the phrase used by the KGB to describe their most valuable assets: the authentic manuscript and typescript reports by the infamous Cambridge spy ring. Many of these reports are reproduced here. As well as adding unsuspected dimensions to the Cambridge ring (including Burgess's offer to murder his fellow conspirator Goronwy Rees), the files reveal a completely unknown Soviet network based in London and headed by a named Daily Herald journalist. They also refer to the huge scale of Soviet penetration of the British Foreign Office from 1927 to 1951; details of a previously unknown spy-ring in Oxford, organized by university undergraduates who went on to work in Whitehall; and the key role played by Anthony Blunt in supervizing post-war Soviet espionage activities in London.