Frank Hudson was a private investigator and one-time employee of Special Agent Pendergast. Short and stocky, Hudson was a former police officer, until diabetes forced him off the street. Unable to handle working behind a desk, he quit the force and went into business as a private investigator. His main client was art dealer and illegal wildlife smuggler John W. Blast, for whom Hudson would perform background checks of potential business partners and suppliers. He drove a vintage Ford Falcon.After Pendergast and Vincent D'Agosta visited Blast during their search for the legendary John James Audubon painting known only as "The Black Frame," Blast—a descendent of Audubon's who had spent twenty years searching for the painting himself—enlisted Hudson to follow the FBI agent, in hopes of relieving him of the mysterious piece should Pendergast be successful in locating it. Pendergast and D'Agosta did manage to find the Black Frame in the basement of Pappy's Donette Hole in Port Allen, Louisiana; Hudson pursued them from Port Allen to Baton Rouge before losing them in the Desmirail Wildlife Area.
After Blast's death, Hudson—under the assumption that Pendergast was Blast's killer—arrived at Penumbra Plantation to blackmail Pendergast for the money Blast owed him in fees and expenses. Pendergast instead hired Hudson as an exclusive investigator, requiring only that he operate without a firearm. His first assignment was to gather information on all of the pharmaceutical companies fifty-mile radius of the town of Sunflower, Louisiana. Pendergast next sent Hudson to the Vital Records Office in Baton Rouge to collect information on June Brodie. While leaving the office, he was shot and killed by a sniper in the parking lot.