The Ninth Man, a modern-day mystery set in Charleston, South Carolina, revolves around a fictional diary kept by a Union spy that explains the disappearance of the H.L. Hunley, a Confederate fishboat that became the world's first successful combat submarine when it sank a Union ship blockading Charleston Harbor. Moze Cheddar, a descendant of the Union spy and an ex-special forces assassin, has found the long lost diary and wishes to keep its contents secret. However, a minister with a passionate interest in the Hunley has learned of the diary's existence and comes to see Cheddar. Soon after, the minister is murdered, and thieves break into Cheddar's cabin attempting to steal the diary. The attempt is unsuccessful, and Cheddar kills one of the thieves. Cheddar traces the thieves to the Charleston area, where he forms an uneasy alliance with Russ Berard, a retired Rhode Island police detective and son of the slain minister. Back home in Charleston after being gone for decades, Berard confronts old memories as he investigates his father's murder and helps Cheddar try to determine who wants the diary badly enough to kill for it. The investigation leads to Berard's first love, now married to a high school friend of Berard's with Mafia connections who is intent on producing a reality show that will belittle the Hunley. In addition, murky and surprising connections between Cheddar and his foes are uncovered. Before Berard and Cheddar work their way through the web of deceit and family relationships, more people die.