PARIS—If you’re going to have an obit in The New York Times, it would be hard have a more intriguing headline than this one from March 2000: “Gertrude Sanford Legendre, 97, Socialite Turned Hunter and Prisoner of War,” unless they’d added, as they should have done, “Spy.”

One might also have said she was spoiled and impetuous and for several months regarded as the greatest potential disaster confronting American intelligence during World War II, or that she was a true heroine who hated being underestimated because she was a woman, but knew the Nazis—even her SS and Gestapo jailors—would do just that, and so survived, and thus kept her secrets.

Gertrude “Gertie” Sanford was born into a very wealthy and well-connected New York family in 1903. Her mother was the daughter of a famous (some would say infamous) diplomat and businessman who founded the town of Sanford, Florida, hoping to make a fortune off of citrus. Her father, a Sanford cousin, manufactured carpets and raced horses in upstate New York.