Professional killer Clayton Drumm is given a reprieve from the hangman's noose when he agrees to hunt down and assassinate rancher Matthew Sebanek. A railroad syndicate wants Sebanek murdered for the crime of refusing to sell his land. Clayton convinces Sebanek to let him stay on and work at the ranch, but instead of shooting his host, he develops a liking for him. When the rancher's sexy young wife, Catherine, seduces Clayton, the lovers flee. Sebanek rounds up a gang of trigger-happy gunmen, who are hell-bent on bringing back the adulterous fugitives, dead or alive.

Cult director Monte Hellman began his career with Beast From Haunted Cave (1959) which was produced by his mentor Roger Corman. He directed a pair of existential westerns starring Jack Nicholson, Ride in the Whirlwind and The Shooting in 1965. Two-Lane Blacktop (1971) is generally considered his best film. In China 9, Liberty 37, Hellman gives one of his heroes, Sam Peckinpah, a bit part as sleazy pulp-western writer Wilbur Olsen.