Mary Surratt was the first woman tried and executed by the United States. She owned and ran a boardinghouse in Washington, D.C. where John Wilkes Booth and other conspirators in the assassination of Abraham Lincoln often met. She was tried and convicted of complicity in Lincoln's assassination and hanged on 7 July 1865. This book portrays her as an innocent victim of a vengeful military tribunal that did not have the right to try her for involvement in the assassination plot. Two subsequent events supported this view. One was the 1866 Supreme Court decision Ex parte Milligan, which invalidated the authority of military courts to try civilians in places where civil courts were functioning.

Ambiguity concerning military and civil authority in Washington, D.C. in 1865 raised questions about the legality of her trial. The other event was the trial of her co-conspirator son, John Surratt, before a civil jury in 1867, two years after her death. Surratt's testimony was similar to that of his mother. When his trial ended in a hung jury, it seemed to many that the military court had executed an innocent woman.