Was Roger Hollis, a key wartime official and later head of Britain's counter-intelligence service, MI5, a Soviet agent? Is that why the Cambridge Ring--Philby, Maclean, Burgess, Blunt--was able to operate with impunity? why so many other security blunders occurred? It was Pincher, Britain's ace spy sleuth, who first disclosed official suspicions, in Their Trade Was Treachery (1981). Now, piqued by Margaret Thatcher's parliamentary assurance that Hollis had been ""cleared"" (when, in fact, ""the case had been left unproven""), Pincher has assembled new evidence of Hollis' possible complicity, to add to old. Hollis apart, it makes a fascinating keyhole dossier on Soviet spydom and British failure to uncover or reveal the penetration. A major weakness of the case against Hollis was his apparent lack of early communist leanings or connections: why would this apolitical Oxford dropout, and bishop's son, have been a Soviet mole? During his nine years in China as a business agent and sometime-reporter, Pincher learned, Hollis met (""clandestinely"") with notorious Soviet agent Arthur Ewert, as well as frequenting Agnes Smedley's salon. There he may also have met Soviet agent Ruth Werner--whose memoirs, published in East Berlin in 1982, provide Pincher with another major building-block. As ""Sonia Beurton,"" Jewish-refugee wife of a British (communist) officer, she took up residence in the environs of Oxford in 1940--just when MI5 was transferred to the vicinity--to transmit radio messages: from Hollis, Pincher presumes. He has one scrap of evidence that might connect them: Igor Gouzenko, the Soviet defector who first told of a Soviet mole inside MI5, also told Pincher of a certain grave-site hiding place used as a drop; and Pincher found a grave in Oxford that exactly matched the curious description. Pincher goes on to Klaus Fuchs, his security clearance by Hollis, and his connection with Sonia; and then to the numerous instances, involving the Cambridge group and others, when Hollis might have leaked information or otherwise blocked action--adding to each chapter an analysis of ""The Potential Value of Oversight,"" his remedy for what he sees as a continuing cover-up. The stories of Hollis' interrogation, of Blunt's confession and concealment, and other glimpeses of behind-the-British-scenes are fully as intriguing as what Hollis may or may not have been up to.