When an old man sees an unidentified Civil War photograph of a woman in the newspaper, he begins a desperate search for a 160-year-old painting that he believes will match the image of the enigmatic woman in the photograph, and if it does, it will prove that his great-great-grandfather did not run from battle. After the old man hires Sean OBrien to find the mysterious painting, OBrien discovers its linked to a secret letter and map that will lead to a trapdoor where a hidden key to the most horrific war on US soil lies buried in mud at the bottom of a river. It's also linked to a new murder, and there are those who will stop at nothing to keep the information hidden because to bring it to the surface will rewrite American history.
