By Alexander Rose.  ISBN-13: 978-0-553-38329-4.  Copyright 2006.  Softcover with 369 pages including notes, bibliography, and index. 

In the summer of 1778, with the war poised to turn in his favor, General George Washington desperately needed to know where the British would strike next.  To that end, he unleashed his secret weapon: an unlikely ring of spies in New York charged with discovering the enemy’s battle plans and military strategy.
The men whom Washington mentored were dubbed the Culper Ring.  The British secret service tried to hunt them down, but they escaped by the closest of shaves thanks to their ciphers, dead drops, and invisible ink.