Chapter One - One - AUGUST 23, 1861 I'm standing on the front step beside Detective Allan Pinkerton, head of Abraham Lincoln's secret service, when our suspect answers the door. She's a handsome woman, somewhere on the far side of forty. Tall, like me, but with an olive complexion, dark hair, and slim build. Dressed in black mourning silk. Does she know who we are? She knows enough to take a paper from her pocket and shove it into her mouth. Right there in front of us, she tries to swallow the damn thing. I lunge over to fish it out. When a suspected spy starts eating messages, you know you've found something.

Pinkerton pushes me toward her. I'm scrabbling at her lips, trying to get my fingers on the evidence. He pushes us both deeper into her house and shuts the front door behind us, so no curious neighbors get to talking. The suspect, the widow Mrs. Rose O'Neal Greenhow, is still trying her damnedest to chew up the paper. I can't get to it. She'll bite off a finger, if she catches one. Pinkerton is hissing directions from the side.

He's not a patient man, my employer. Finally, he shoves me aside and gets in there himself. He cradles the woman's head in his hands just like a baby and jams a sausage-sized finger in through the space of a pulled back tooth. And he does it: He pries the woman's jaws open and fishes out the message. Well, half the message. "You must be iron-willed." He waves the soggy mess of chewed paper in my face. The widow is a bent heap of fury beside him.

There's enough of the letter left to see it's enciphered. And there's hardly a doubt it's a Confederate cipher. We found our spy. About two minutes later, Pinkerton puts the widow under house arrest in her own parlor. It's an incredible piece of luck finding our evidence so quickly. But that's just the beginning of the work. Our job now is to get the woman's cipher key. Most people cannot commit an entire cipher to memory, so they keep a key written down.

We find that, we can intercept Confederate intelligence regarding their next moves. But the moment we put Widow Greenhow under arrest, the clock starts ticking. We've got a narrow window of time before anyone discerns she's been compromised and the cipher gets changed. Now, we've exercised extraordinary care in the widow's capture. And Pinkerton has given orders to sequester any persons who come knocking at her door, be it the milk boy or some big bug, so as to keep word of the woman's arrest within these walls. As long as the widow doesn't start sending smoke signals, we've got ourselves a window. How long? Pinkerton estimates it at about two days. We could end the whole war right here from this house.

That's our aim.