Washington has fallen! Legions of 'grays'—dead soldiers reanimated on the battlefield and pressed back into service of the Southern Cause—have pushed the lines as far north as the Ohio River. Lincoln has moved the government of the United States to New York City. He needs to stop the juggernaut of the Southern undead 'abominations' or the North will ultimately fall. But Allan Pinkerton, his head of security, has a plan... The Northern newspapers are heralding Braxton Wright as the Hero of Parkersburg, but the engineer who designed the Northern walking monitors—Tall Guns—knows the truth. He acted more out of panic than heroism and is certain he got his best friend, physician Lawrence Hancock, killed in the cold waters of the Ohio as a result. What he would like is to be forgotten. But at Pinkerton's urging, Lincoln sends Braxton on a mission aboard General Sherman's airship deep into Southern territory. He will find Hattie Lawton, the woman who is the North's most capable spy, and together, they must stop the Southern undead from rising again!

On the run! Union Engineer Braxton Wright thought his mission into the south was to extract the contents of a top secret Confederate train. Unbeknownst to him, he was a just a pawn in Alan Pinkerton’s plan to break his ace spy Hattie Lawton out of the Castle Thunder Prison. Now free, and in the company of Braxton’s childhood friend Laurie as well as a mysterious metal man, Braxton is itching to return north to his safe, quiet drafting board. But Hattie has other plans. Pinkerton didn’t arrange for her escape for no reason. She has something that the Union has been searching for since the start of the war—the location of the Alchemist who invented the Gray soldiers. With the might of the Confederate army on their tale, Hattie and Braxton must make their way deep into the heart of the south and find the man who’s twisted genius brings dead soldiers back to serve. If Braxton can discover his formula, they just might be able to counter the Confederacy's’ greatest advantage. Nipping at their heels, Colonel Beauregard Fuller of the Confederate Engineering Bureau also has a plan. If his agent can capture Braxton, the Union engineer might just be persuaded to serve him. With Braxton’s knowledge, the South could develop their own walking guns. With guns, Grays, and their dragons, the Union would have no hope of victory and be forced at last to let the Confederacy go!