The world was at war, America precariously poised on the sidelines. But already a second secret war was well underway. While he fought on the home front to consolidate the FBI’s intelligence gathering power, J. Edgar Hoover was conducting an all-out campaign to make his agency America’s first foreign espionage service - a campaign that would lead to an uneasy alliance with British intelligence in a brilliantly successful operation to undermine Germany.

Taking up the tale begun in his acclaimed Origins of FBI Counterintelligence, FBI historian and former agent Raymond Batvinis mines a wealth of heretofore untapped resources to expose Hoover’s remarkable connivances and accomplishments in concert - and occasionally contention - with the Allies in outsmarting German intelligence. Hoover’s Secret War opens up a world of spy rings, secret and double agents, surveillance, codes and ciphers, wire taps, micro dots, mail drops, invisible ink, radio transmissions and deception and disinformation as it tracks the warring nations spreading their intelligence tentacles throughout Europe and North and South America. As it documents the rocky evolution of the FBI’s relationship with Britain’s vaunted MI5 and MI6, the book brings to light the feud between Hoover and Williams Stephenson, director of the British Secret Intelligence Service’s U.S. operation.

Batvinis reveals how the agency gained access to ULTRA intelligence. He uncovers eye-opening details of the FBI’s participation in the famed “Double-Cross"" System, which effectively “turned” German agents against the Fatherland, among them a flamboyant, larger-than-life playboy, a world famous French flyer and a lecherous Dutchman. Batvinis tells for the first time how the Bureau manipulated these agents and how it transmitted deceptive information critical to the Normandy landings, the Allied invasion of the Marshall Islands and the atomic bomb programme, among other matters. Rich with secrets and surprises worthy of the finest spy fiction, this true story of espionage and counterintelligence gives us our first clear look at the secret second world war and a significant moment in history.