Max Hastings is tickled by the irony that Alan Turing, the brilliant mathematician codebreaker at Bletchley Park during World War II, has emerged as a celebrated secret warrior, when until recently he was virtually unknown outside his professional circles. Yet this is appropriate. This was the conflict when signals intelligence - the art of analysing wireless communications - came into its own. Despite extensive networks of spies and resistance fighters, the meticulous work at Bletchley Park and its American equivalent, Arlington Hall, changed the course of events. Boffins such as Turing have in many ways superseded cavalrymen and fighter pilots as military role models.
Hastings made his name with his histories of active combat. This is his first sortie into the secret world, and that background shows, as he puts the codebreakers' achievements in context by measuring them against competing sources of secret intelligence - not just in Britain but in the other main belligerent countries, including Germany, the Soviet Union, Japan and the United States. The result is authoritative, exciting and notably well-written.
Of these other participants, the Russians come out of the hostilities most creditably. Their agents were active in Britain and the United States throughout the war, and alerted Stalin to the Allies' progress on the atom bomb.
It is chastening to learn that from 1936 Britain's Secret Intelligence Service (SIS or MI6) had no station in the Soviet Union, while in 1941 their Russian equivalents in London forwarded to Moscow 7867 British classified documents, 715 on military matters, 51 on intelligence, 127 on economics and the rest on political and other subjects.
Capitalising on their many ideological fellow travellers, the Russians also ran successful espionage networks with exotic names such as the Red Orchestra, which operated in Germany. They were skilled at deception, though often at a terrible price to their own side. Hastings describes how the Russians sacrificed 70,000 people in an elaborate feint to deceive the Germans around Stalingrad. And he recounts the story of their agent, "Max", who convinced the Nazis he was part of a right-wing anti-Soviet conspiracy, known as The Monastery.