As a native New Yorker, I always found Rockefeller Center to be a romantic place, with skaters on its outdoor ice rink and a giant Christmas tree towering high into the air during the holidays. Years ago, I even proposed marriage to my future wife there amid the thousands of tourists strolling by.

Yet I had no idea it was once a hotbed for spies in the heart of Manhattan during World War II. The secret violence, sex, and intrigue of this place didn’t become apparent to me until I began research for my new biography, The Invisible Spy: Churchill’s Rockefeller Center Spy Ring and America’s First Secret Agent of World War II.

This book tells the largely unknown story of Ernest Cuneo, an ex-N.F.L. player who became a White House insider and the first American spy of World War II. Cuneo, a Democratic Party lawyer and part of President Roosevelt’s “Brain Trust” of aides and advisers, worked with a British spy ring authorized by Winston Churchill in 1940.

Known as the British Security Coordination, the ring operated secretly out of Rockefeller Center in the days before Pearl Harbor. Its official purpose was to stop Nazi spies in the United States from sabotaging vital supply lines to Britain. Soon, however, the B.S.C. was interfering in Congressional elections against isolationist candidates and implementing propaganda campaigns to convince America to join the war, when public opinion was largely against it.

In his work with the B.S.C., Cuneo became friends with a British naval-intelligence officer named Ian Fleming, later helping Fleming to write his James Bond spy novels. Thunderball, the eighth novel in the series, is dedicated to Cuneo.

However, my favorite relationship from the book is Cuneo’s romance with another of Churchill’s spies—Margaret Watson, a 28-year-old secretary from Canada, was one of the many female agents stationed at Rockefeller Center during the war. These women had a variety of jobs, from clerical work managing the huge amount of top-secret information, to serving as agents in the field, using their wits and allure to secure secrets from foreign dignitaries.

Though Watson’s official job was secretary, her espionage abilities far exceeded her administrative ones.

“She had top secret clearance and was one of the people who knew what was really happening,” explained her daughter, Sandra, years later. “If you told my mother a secret, and told her not to tell anybody, it went into a lockbox, never to be heard from again. She never betrayed a secret.”

Before she met Cuneo, Watson had been recruited by the Canadian spymaster William Stephenson—known by the code name “Intrepid”—who oversaw the super-secret British Security Coordination operation. Stephenson, a Canadian World War I fighter pilot and a friend of Churchill’s, recruited many women like Watson from Winnipeg and elsewhere in Canada to work for the B.S.C.. (It was believed Canadians would blend into American life more easily without detection than the British agents.) Located on the 36th floor of the International Building at Rockefeller Center, the B.S.C. kept away nosy New Yorkers by posing as the British Passport Control Office.

Soon after her arrival in New York, Watson learned that life as a spy can be dangerous. Along with other female spies working for the B.S.C., Watson lived in a nearby dormitory-like building. One night, 1941, while asleep in bed, Watson suddenly awoke to the overwhelming force of a man pinning her body to the mattress. The intruder grabbed her pillow and shoved it onto her face. The terrifying blackness, and no air to breathe, made her frantic.

Using every ounce of strength in her arms and legs, Watson eventually wriggled free. She fought off her attacker until her screams alerted a dormitory guard, who pulled the assailant off her. Soon other security officers arrived and wrestled the attacker to the floor.

The intruder spoke only a few words—garbled, but clearly with a German accent—before being whisked away by British agents. New York police were never called, and the German agent was never seen again. He was most likely “dispatched,” to use the lethal euphemism of the time.

The intruder specifically wanted “to kill her, not rape her—kill her,” recalled Watson’s son, Jonathan, who heard the story directly from his mother years later. “It didn’t end well for him. I don’t think he was let go that night, let’s put it that way.” Watson was singled out for attack in the secure British-run dormitory, her son theorized, because she was by then involved in tracing the flow of Nazi banking funds abroad.

“Her role in British intelligence dealt with South America, and it dealt in a large part with banking operations,” recalled Jonathan.

In early 1942, Watson was introduced to American spy Ernest Cuneo at the B.S.C.’s Rockefeller Center headquarters, and the couple eventually married in 1946. But both Margaret and Ernest spoke little about their spy careers to others after the war, honoring the code of silence surrounding their service. Indeed, only decades later did their children, Jonathan and Sandra Cuneo, by then both adults and accomplished lawyers, learn about their mother’s near-death experience while working with Churchill’s spies.

Thomas Maier is an Emmy-winning television producer, a journalist for Newsday, and the author of several books