During a failed raid to free northern POWs in 1864, papers are found on the body of Union Colonel Ulric Dahlgren ordering the assassination of Confederate President Jefferson Davis. The discovery fuels outrage in the South and energizes the Confederate secret service. The Dahlgren Affair may have changed the course of the American Civil War. Now, historians have teamed up with descendants of the slain colonel to uncover who was behind the audacious murder plot and to consider if Abraham Lincoln's assassination one year later may have been a retaliatory measure.