Sally Townsend of Oyster Bay was a petite, vivacious, intelligent and remarkably beautiful young lady with beguiling eyes. A 1779 Valentine poem from an admiring British officer reads: "Thou know'st what powerful magick lies Within the round of Sarah's eyes."

She was the sister of Robert Townsend, a principal member of the "Culper Ring," General Washington's most effective spy network. During the British occupation (1776-1783), Loyalist and Hessian troops were quartered in and around Oyster Bay, two Redcoat officers in the Townsend home.

Sally assisted her brother in gathering intelligence while coyly flirting with the enemy. The romantic interest of Jager officer Ernst Wintzingerode, she dallied with Major John Andre and was courted by Lt. Col. John Graves Simcoe of the Queen's Rangers. She paid a heavy price for her role in thwarting the Benedict Arnold treason plot.

The book explores the possible identity of the mysterious "Agent 355" mentioned in a cryptic Culper Ring message.