My family has tenuous links to the Culver Spy Ring through my mother's grandfather, Frank Garfield Beers, who was descended from Andrew Eliot, D.D. through his daughter Sarah, who married Joseph Squires of Fairfield. The Squire descendents eventually married into the Beers family.
Andrew Eliot D.D. was the pastor of the New North Church in Boston and was one of the few ministers who remained in the city during the Revolutionary War (the letters shown were sent to his son describing the seige).
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His son and Sarah's brother, also named Andrew, was minister of the Congregational Church in Fairfield, Connecticut. There are a series of letters written from the younger Andrew to his father that refer to the spy activities going on in Fairfield at the time. A book called Missing Links to the Culper Spy Ring by Bernadette Fawcett details the letters and shows how involved the Eliots were in the spy ring.
As I said, the TV show is excellent and I heartily recommend it to lovers of American history.