Following the assassination of President Abraham Lincoln, a nation grapples with the aftermath of the shocking event. Eight individuals are arrested, accused of conspiring to kill the president, vice president, and secretary of state. Among them is Mary Surratt, the owner of a boarding house where the conspirators reportedly met. Frederick Aiken, a war hero and young lawyer, reluctantly agrees to defend her, believing her to be nothing more than a scapegoat. As Aiken delves deeper into the case, he finds himself questioning her guilt and the fairness of the military tribunal set against her.

As the trial proceeds, Aiken faces mounting pressure from all sides— his peers, public opinion, and the government, which is eager to swiftly conclude the case. Aiken's struggle intensifies as he battles not only for Surratt's life but also for the principles of justice in the fledgling post-war society. He discovers disturbing evidence that suggests Mary's son, John Surratt, might be the real orchestrator of the plot, forcing Aiken to challenge his beliefs and take significant personal and professional risks. The narrative examines themes of justice, loyalty, and the intricate web of political manipulation, leaving the ultimate question of Mary Surratt's true role shrouded in ambiguity.