Most World War II spies learned little of import—and those who did were invariably disbelieved.

Any historian who hopes to tell the true story of secret intelligence operations, even from the distant past, quickly discovers that he is up against two formidable obstacles.

First is the Kafkaesque system of government classification. Not only do U.S. intelligence agencies routinely refuse to declassify material from 70 or more years ago, they have taken to reclassifying and removing from the National Archives some previously released World War II-era files.

The other problem is that spies are professional, if not congenital, liars.

In the introduction to his sprawling, revisionist-tinged history of espionage, cryptanalysis, and partisan warfare in World War II, British historian Max Hastings quotes the cautionary words of Malcolm Muggeridge, who worked for the British secret service during the war. Intelligence work, Muggeridge said, “necessarily involves such cheating, lying, and betraying that it has a deleterious effect on the character. I never met anyone professionally engaged in it whom I should care to trust in any capacity.”