With the Confederate Army firing on Fort Sumter, the Civil War has begun - and an invasion of Washington, DC, from Secessionist Virginia seems imminent. As the population evacuates, the president is in desperate need of men to defend the capital.

Lincoln's trusted aide, Adam Speed Quinn, and Quinn's old friend from the Bloody Kansas conflict, Senator Jim Lane, hastily assemble a motley crew of just over a hundred men and garrison them in the East Room at the White House itself. Dubbed the Frontier Guard, these rough-and-tumble patriots steel themselves for the inevitable attack.

But even as dawn breaks with no Rebel strike, a single act of violence intrudes within the White House. One of the Frontier Guard lies dead in the oval library, throat slit ear to ear. There is a murderer among them.

Lincoln promptly assigns Quinn to deal with the matter, who is in turn aided by journalist Sophie Gates and Dr. George Hilton. And to Quinn's chagrin, the Southern belle Constance Lemagne insists on being involved in the investigation as well. But when Dr. Hilton examines the body, he makes a startling discovery that overturns all Quinn's assumptions about the murder. With his president at grave risk from without and within, Quinn must act quickly to catch the White House killer....