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 juggernaught 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!