Before leaving Washington to become the Adjutant General of Beauregard's army Colonel Thomas Jordan had given her the cipher code of the South and arranged to make her house the Northern headquarters of the Southern secret service.
Her first messenger was a girl carefully disguised as a farmer's daughter returning from the sale of her vegetables in the Washington market. She passed the lines without challenge and delivered her message into Beauregard's hands.
With quick decision Beauregard called his aide and dispatched the news to the President at Richmond:
"I have positive information direct from Washington that the enemy will move in force across the Potomac on Manassas via Fairfax Court House and Centreville. I urge the immediate concentration of all available forces on my lines."
The Southern commander began his preparations to receive the attack.
The house on Church Hill had not been idle. Richmond swarmed with Federal spies under the skillful guidance of Socola.
General Scott knew in Washington within twenty-four hours that Beauregard was planting his men behind the Bull Run River in a position of great strength and that the formation of the ground was such with Bull Run on his front that his dislodgment would be a tremendous task.
The advance of the Federal army was delayed—delayed until the last gun and scrap of machinery from Harper's Ferry had been safely housed in Richmond and Fayetteville and Johnston had withdrawn his army to Winchester in closer touch with Beauregard.
And still the Union army did not move. Beauregard sent a trusted scout into Washington to Mrs. Greenhow with a scrap of paper on which was written in cipher the two words:
"Trust Bearer—"