For almost half a century, Bertram Mills Circus was a household name throughout Britain among both children and adults.Cyril Bertram Mills, circus director and son of the founder, was one of the best-known and most influential personalities in the country's entertainment business.But for forty years, Cyril Mills also pursued a top-secret, wide-ranging career in British intelligence, obtaining the best aerial intelligence on Nazi rearmament for MI6; recruiting GARBO, the best double agent of the Second World War; and working part-time during the Cold War 'for MI5 or 6 or both without being paid a penny'.Remarkably, no word of Mills's secret career appeared in public until he was over eighty.Nobody suspected that the glamorous world of the pre-war circus had been an extraordinary rehearsal for the top-secret arena of surveillance and deception.In this incredible true story, Christopher Andrew, former official historian of MI5 and bestselling author, in collaboration with ex-KGB officers, of histories of Russian intelligence, brings to life one of the most surprising and fascinating careers in British espionage.