In the wake of Abraham Lincoln's assassination, seven men and one woman are arrested and charged with conspiring to kill the President, Vice-President, and Secretary of State. The lone woman charged, Mary Surratt, 42, owns a boarding house where John Wilkes Booth and others met and planned the simultaneous attacks. Against the ominous back-drop of post-Civil War Washington, newly-minted lawyer, Frederick Aiken, a 28-year-old Union war-hero, reluctantly agrees to defend Surratt before a military tribunal. Aiken realizes his client may be innocent and that she is being used as bait and hostage in order to capture the only conspirator to have escaped a massive manhunt: her own son.