The legendary mysteries of British Intelligence, briskly and soberly laid out by the historian also of M 15, Britain's internal security service. West begins with the formation of the Secret Intelligence Service (SIS) in 1909, and blocks in its WW I successes on the Western Front and doomed attempts to overthrow the new Soviet regime (including two tries at assassinating Lenin). These anti-Bolshevik efforts had disastrous issue in the 1924 Zinoviev affair, when a forgery (by fanatic/adventurer Sidney Reilly, ex of SIS) led to election of a Conservative government. A small, viable overseas intelligence network was built up in the 1920s, under cover of Passport Control Offices; but much time was spent collecting ""misinformation about Russia""--from neighboring countries--and very little on monitoring the Nazi rise to power. SIS history in the '30s was ignominious: a flood of Jewish visa applicants led to bribery scandals at lower levels; insufficient funds, and a shortage of qualified personnel, climaxed in a major hoodwinking by the Nazis; the Russian fiascos, and SIS failure to foresee the Abyssinian and Rhineland moves, cost it credibility, so that valid warnings of German rearmament were not believed. West does credit SIS head Hugh Sinclair with recognizing that war was inevitable, and setting up two salient units: Section D (later known as Special Operations Executive), to foster subversion and conduct guerrilla operations; and Section V, for counter-intelligence. Sinclair's death then brought Stewart Menzies, and a reinvigorated SIS--more, West seems to think, because of Menzies' canniness in insinuating himself with Churchill (and winning over the Foreign Office, Donovan of the US), than from any flair for espionage or management. But the book is almost an institutional history: West chronicles WW II operations theater-by-theater--with organizational charts, names and code names. There is a vast amount of new detail, a high level of frankness, and little drama. For the espionage adept, it's a must; others may prefer to wait for narratives with more focus, color, and shape.