Set against the backdrop of the Civil War, The Assassin's Accomplice tells the gripping, true story of the conspiracy to assassinate Abraham Lincoln through the eyes of its only female participant, the first woman ever to be executed by the federal government of the United States.

Mary Surratt, a Confederate sympathizer, ran the boardinghouse in Washington where the conspirators, including her rebel son, John Surratt, met to plan the assassination. The depth of Surratt's complicity in the assassination of President Lincoln has been debated since the day she was arrested on April 17, 1865, three days after John Wilkes Booth murdered Lincoln as he sat watching a play at Ford's Theatre. Less than three months after her arrest, Mary Surratt would hang. The military tribunal that found her guilty never doubted their decision, but five of the nine commissioners petitioned President Andrew Johnson, Lincoln's successor, to show mercy because of her sex and age. President Johnson, however, was unmoved, convinced that Surratt "kept the nest that hatched the egg."

Based on long-lost interviews, confessions, and court testimony, this book reveals Mary's deep complicity in the murder plot, and explores how Mary's actions defied nineteenth-century norms of femininity, piety, and motherhood, leaving her vulnerable to deadly punishment historically reserved for men.