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.