Riddle of the Confederate Spy

Cannons fired in Maryland, as 45,000 Confederate soldiers crossed the Potomac River,
approaching Washington, D.C.

But far away in Illinois, a lonely Union sergeant performed his own duty – guarding a secluded stretch of railroad tracks against sabotage. It had only been one week, and already he missed home.

That night, the sergeant’s troubled eyes searched the sky for answers, while the campfire cast shadows on the faces of four soldiers who accompanied him. “You're all good soldiers,” Sergeant Stoker said, fondly. “Unfortunately, one of you is a spy.”