Former Pinkerton Agent Nessa Donnelly has nearly forgotten life before trading in her skirts for her brother's suit. As “Ness Donnelly”, she’s become Kentucky's most prominent detective, but her success is built upon a foundation of lies. Now she must help Doc Haydon, the county medical examiner, identify a murder victim discovered in the ashes of Lexington's Phoenix Hotel. The victim is Fergus O’Brien, Mary Katherine McGuire’s uncle. Nessa first met Mary Katherine on a blind date, and their relationship bloomed. Beulah, her beloved housekeeper and ally, warns Nessa that she is creating expectations, but Nessa waves her off.
Unfortunately, evidence from the hotel room puts Mary Katherine at the scene on the night of the fire. The more Nessa learns, the stronger the case against Mary Katherine grows. Worst of all, though, Doc Haydon has taken an interest in Mary Katherine himself – which bothers Nessa far more than she thinks it should.
When a colored boy is charged with murdering O’Brien, a white man, Nessa’s first reaction is relief. Professor Percival Pettijohn, a quirky inventor, pleads with Nessa to save Jake, his young assistant, from the gallows. The lad had good reason to kill O'Brien, but Pettijohn is certain he was framed. Nessa is reluctant to help until she discovers that Pettijohn's assistant is Beulah’s grandson.
Haydon, Donnelly, and Pettijohn put their lives on the line as a mob attempts to lynch the youngster. Stopping the mob once is not enough; O'Brien was involved with the Red Strings, a vigilante group with Northern sympathies. They show up in force, along with their mortal enemies, the Ku Klux Klan. Finding the real killer is the only hope Jake has, but this means Nessa must place herself between the Klan and the Red Strings.