The story is told through the eyes of its protagonist, Lou Ford, a 29-year-old deputy sheriff in a small Texas town. Ford appears to be a regular, small-town cop leading an unremarkable existence; beneath this facade, however, he is a cunning, depraved sociopath with sadistic sexual tastes. Ford's main outlet for his dark urges is the relatively benign habit of deliberately needling people with clichés and platitudes despite their obvious boredom: "If there's anything worse than a bore," says Lou, "it's a corny bore."
Despite having a steady girlfriend, Ford falls into a sadomasochistic relationship with a prostitute named Joyce Lakeland. Ford describes their affair as unlocking "the sickness" that has plagued him since adolescence, when he sexually abused a little girl, a crime for which his elder foster brother Mike took the blame to spare Lou from prison. After serving a jail term, Mike died at a construction site. Lou blamed a local construction magnate for Mike's death, suspecting he was murdered.
To exact revenge, Lou and Joyce blackmail the construction magnate to avoid exposing his son's affair with Joyce. However, Lou double-crosses Joyce: He ferociously batters her, and shoots the construction magnate's son, hoping to make the crimes appear to be a lovers' spat gone wrong. Despite the savage beating, it's revealed that Joyce survives, albeit in a coma.
Ford builds a solid alibi and frames other people for the double homicide. However, to successfully frame others when the evidence starts to go against him, he has to commit additional murders. These only increase suspicion against him however, and his mask of sanity begins to crumble under the pressure.