Murphy came out of the Civil War a bitter, disillusioned man after his family was murdered while he was on the battlefield. He spent years tracking the Army deserters responsible for the death of his family. After he caught up with the last of them, Murphy went to Washington to serve in the Secret Service under President Grant. When Grant's term in office was over, Murphy returned to his native state of Tennessee where he ran for Congress and won a seat in Washington. Called back into service by President Garfield, Murphy resumes his role as Regulator and takes on a top secret assignment. A serial killer is murdering railroad workers and settlers out west. Murphy travels to New Mexico, and using his knowledge of the budding science of forensics, studies ballistics, fingerprints, and victims to track down and stop the killer.