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Lou Ford, a deputy sheriff in Central City, Texas, is sent to run a prostitute named Joyce Lakeland out of town, begins an affair with her, and uses her in a plan to kill Elmer Conway, son of the local magnate he blames for his brother Mike's death. Each later killing, including the young Johnnie Pappas hanged in a jail cell and his fiancée Amy Stanton, is committed to cover the previous one, until the net closes and the novel ends in a fire.
Lou presents himself as a slow, amiable bore who speaks almost entirely in homespun clichés. Because people discount someone they find tedious and harmless, they stop watching him, and the persona becomes the cover under which he plans and kills. He also uses the clichés as a private weapon, needling listeners with platitudes they cannot object to without seeming rude.
The novel is narrated by the killer himself in a chatty, reasonable, self-justifying voice, so the reader is drawn into his logic before the violence arrives. His own account keeps exposing contradictions, rationalizations, and things he misreads or leaves out. The gap between how calmly Lou describes events and what he is actually doing is where the horror comes from.
Once a crime has to be hidden, each person who might expose it becomes a new threat that has to be removed. Every cover-up widens the circle of people who know something, so the killings multiply and grow more reckless rather than stopping. Lou ends up destroying the people closest to him while still insisting he is in control.