At the start of the American Civil War, Professor John Ulysses Martin of Clarksville, Tennessee and his students march off to face the harsh reality of battlefield combat. As his students die one by one, John questions his lofty convictions and, after losing a leg at Antietam, realizes he has made a fool of himself. He concludes that war is nothing more than the butchery of innocents. During his convalescence at Armory Square Hospital, John makes notes in a pocket Bible of Yankee troops and artillery heading south for an attack on Richmond. Caught spying, he is taken to the Old Capitol Prison to be hanged, but manages a harrowing escape. When he reaches Richmond and turns in his notes, General Hood realizes John's value to the war effort and rewards him with a perilous assignment: destroy the railroad bridge over the Cumberland River at Clarksville, Tennessee.