Oleg Vladimirovich Penkovsky, regarded by many as one of the most beneficent agents in the history of espionage, was tried and sentenced to death in Moscow in 1963. Having only by a near miracle escaped that very fate myself in 1985, I naturally have a close personal interest in the subject of this monograph. Half a century after Penkovsky’s death, and with Putin’s intelligence organisations working very energetically against their Western ‘partners’, it is well worth re-examining all the available evidence (a good deal of the relevant material has not yet been declassified), consulting the surviving Western participants in the Penkovsky operation and trying to find convincing answers to at least three of the still inadequately explained mysteries. Why exactly did Penkovsky offer his services to the Americans in August 1960? If not from the very start, how soon and thanks to whom did the KGB or the GRU (military intelligence) find out what he was doing? And is it an exaggeration to claim that, but for his great sacrifice, a third world war might or would have broken out during the Cuban Missile Crisis of 1962?