On Aug. 23, 1862, Allen Pinkerton and several of his agents went to a fashionable house on 16th Street in Washington and placed the owner under house arrest on charges of espionage. The news sent shock waves through the capital, for the suspect was one of the city's prominent hostesses, Rose O'Neal Greenhow, a woman in close terms with men in Congress and the Cabinet.
Born in Maryland, Rose O'Neal was the aunt of a powerful U.S. Senator Stephen A. Douglas. She married Robert Greenhow, a Virginia-born physician and State Department linguist. Following his death in 1854, the 40-year-old widow was left with four children and her fine home, where she entertained friends in high places. Politicians, soldiers, and diplomats mingled regularly in her parlors. Massachusetts Sen. Henry Wilson, chair of the Military Affairs Committee, was a frequent guest and ardent admirer. She was formidably intelligent, well informed and adapt at intrigue.