April 13, 1861: Rebel troops are across the Potomac River, only 800 feet from the White House and President Lincoln--but a murderer is even closer . . .

As the Civil War begins, an invasion of Washington, D.C., seems imminent. Lincoln's trusted aide, Adam Speed Quinn, and Quinn's old friend, Senator Jim Lane, hastily assemble a motley crew of just over 100 men and garrison them in the East Room at the White House. But even as dawn breaks, a single act of violence intrudes. 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. To Quinn's chagrin, 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 . . .