After the Lloyd Hopkins Trilogy, written in the third person, Killer on the Road returns to the first-person narrative style of Ellroy's first two novels. For the first time in Ellroy's career, however, the story is written from a criminal's point of view.
Killer on the Road tells the story of a serial killer named Martin Plunkett. Plunkett is the typical criminal of Ellroy's early fiction: a psychopath with an outstanding intelligence and a homosexual streak.
Plunkett engages on a career of housebreaking and murder, gaining knowledge from the police officer who acts as a foster father to him after he has killed his mother. Plunkett avoids detection for years by keeping a low profile, staying an odd-jobber and traveling across the U.S. aboard his "Deathmobiles" I and II.
Plunkett escapes the law once when he is detected by Sergeant Ross Anderson of the Wisconsin State Police, who turns out to be a fellow serial killer who "[likes Plunkett's] style." The two become more or less romantically involved and Anderson protects Plunkett as best he can.
After FBI agent Thomas Dusenberg finally detects him, Plunkett is sentenced to four consecutive life sentences, which he serves in Sing Sing. This is where he writes his memoir, whose form the novel assumes.