The film opens with a mysterious harmonica-playing gunman, whom Cheyenne later dubs "Harmonica", shooting three men sent by Frank to kill him. In a roadhouse on the way to Sweetwater, where he also encounters Mrs. McBain, Harmonica informs Cheyenne that the three gunfighters appeared to be posing as Cheyenne's men. Cheyenne arrives at Sweetwater soon after, and both men seem attracted to Mrs. McBain. Harmonica explains that according to the contract of sale, she will lose Sweetwater unless the station is built by the time the track's construction crews reach that point, so Cheyenne puts his men to work building it.