In his book “Writer, Sailor, Soldier, Spy: Ernest Hemingway’s Secret Adventures, 1935-1961,” Nicholas Reynolds chronicles Hemingway’s suspected espionage work for both Soviet and U.S. intelligence agencies, before and during the Cold War. A military historian and former U.S. Marine colonel, Reynolds also spent more than a decade as a CIA officer.

In 2010, he was curating an exhibition at the CIA Museum about the Office of Strategic Services (OSS), the nation’s first intelligence agency, and its origins during World War II. In the process, he found himself wondering whether the famously adventure-seeking Ernest Hemingway had ever done work for the OSS. After all, this freewheeling forerunner of the CIA had counted Julia Child, director John Ford and other prominent Americans among its ranks.

When Reynolds looked into it, he found evidence suggesting that Hemingway had in fact been involved in work for the OSS as well as other U.S. agencies, including the FBI, the State Department and the Office of Naval Intelligence (ONI). But in a stunning twist, he also found evidence that beginning in late 1940, Hemingway may have spied for another organization—the People’s Commissariat for Internal Affairs (NKVD), which was the predecessor of a more widely known Soviet intelligence agency, the KGB.

The revelation that one of his literary heroes may have spied for Joseph Stalin’s Soviet regime hit Reynolds hard. “I felt like I had taken an elbow deep in the gut when I read he had signed on with the NKVD,” he writes in the introduction to his new book.”

As Reynolds recounts, Hemingway wasn’t particularly political, until the Spanish Civil War broke out in 1937. While reporting on the conflict for the American Newspaper Alliance, Hemingway became passionately devoted to the anti-fascist cause, and even joined the republican guerrillas fighting Francisco Franco’s nationalist forces. He would later draw on the experience when writing “For Whom the Bell Tolls,” one of his most acclaimed novels.

His experience in Spain plunged Hemingway into the world of the revolutionary left, and brought him to the attention of the Soviets. The Soviet Union was the only foreign power to provide real support to the Spanish rebels, while Nazi Germany and Fascist Italy backed Franco.

In a 2009 book written by an estranged former KGB officer, Alexander Vassiliev, Reynolds found “verbatim excerpts from Ernest Hemingway’s official Soviet file that Vassiliev had smuggled out of Russia.” The excerpts showed that around December 1940, NKVD agents had recruited Hemingway for “our work on ideological grounds.” Though it’s unclear what exactly they wanted from Hemingway, his influence and access, as well as his talent as a propagandist, would have made him a potentially valuable intelligence asset.

According to the smuggled file, Jacob Golos, a top agent in the NKVD office in New York, was the one who met with Hemingway, who received the code name “Argo.”

“The deal got sealed here in New York, somewhere on the Lower East Side. We don’t know exactly,” Reynolds told CBS News. Although Hemingway apparently met several times with the Soviets during the 1940s, he may have ultimately done little to help them. As Reynolds sees it, he seems to have been motivated more by his opposition to fascism than any particular allegiance to communism and likely regretted entering into the arrangement as more time passed.

With World War II heating up, Hemingway also seems to have gotten involved with U.S. intelligence, participating in several missions for the OSS. For one of them, Reynolds recounts, Hemingway set out to chase German U-boats in the Caribbean after outfitting his cabin cruiser, Pilar, with the help of the Office of Naval Intelligence.

While the United States and USSR were on the same side in World War II, things changed quickly after the war ended in 1945. With the dawn of the Cold War and particularly during the Red Scare of the late ‘40s and ‘50s, Hemingway’s ties with Soviet intelligence would come to haunt him. As Reynolds sees it, Hemingway’s involvement with the NKVD “influenced many of the decisions he made during his last fifteen years: where he lived, what he wrote, and how he acted.”

Hemingway wrote little about his espionage activities —at least in the writings he published. In letters to his close friends, however, Reynolds says he shared concerns about how his past work with the Soviets might make him a target for Sen. Joseph McCarthy and other anti-communist crusaders. In fact, such worries may even have played into the increasing paranoia Hemingway suffered in the last year of his life, up until he committed suicide in July 1961.