At an airstrip near the California-Mexico border Wyatt and Billy, two motorcyclists, sell a large quantity of cocaine to a pusher who handles the transaction from his chauffered Rolls Royce. Once Wyatt (who is called Captain America because of the stars and stripes on his jacket and bike) has concealed the cash in his cycle's gas tank, the two young men ride off, vaguely intending to reach New Orleans in time for Mardi Gras. Unwelcome at motels because of their nonconformist appearance, they camp outdoors and smoke marijuana until they fall asleep. After stopping at a ranch where they repair their bikes and join the rancher and his Mexican wife for a meal, they pick up a hitchhiker and accompany him to the commune where he lives. Despite the friendliness of the people working the barren soil and a pleasant swim with two women, Billy becomes impatient to leave, and the two once more take to the road. Upon arriving in a Texas town, where a civic celebration is in progress, Wyatt and Billy join the procession and are jailed for "parading without a permit." Sharing their cell is alcoholic George Hanson, a civil rights lawyer who prefers sleeping off his binges in jail to facing the wrath of his wealthy father, one of the town leaders. A quick camaraderie develops among the three men; George intercedes and prevents jail officials from giving the two traditional haircuts, and he accepts their invitation to ride with them, mainly because he has always wanted to visit the House of Blue Lights in New Orleans. One night while sitting around a fire, George smokes his first joint and joyfully elucidates his theory that creatures from Venus are already living among us. The next day the three travelers stop at a small luncheonette but leave when confronted by open hostility and bigotry. That night they are attacked at their camp site by thugs who pummel George to death and leave Wyatt and Billy badly beaten. Incapable of voicing their feelings, Wyatt and Billy pay tribute to George by riding on to New Orleans and visiting the House of Blue Lights. Finding that neither the prostitutes nor the Mardi Gras festivities can overcome their moroseness, they go to a nearby cemetery to take LSD with two of the prostitutes. When the acid trip turns out to be a bad one that leaves Wyatt and Billy more despondent than before, they take to the highways again. Though Billy suggests they change direction and head for Florida, Wyatt senses the futility of continuing. The next morning they are passed on the road by two men in a pickup truck who decide to scare the two longhairs by pointing a shotgun at them. When Billy responds with a gesture of defiance, one of the men fires a shot that hits him in the stomach. After trying to reassure his dying friend, Wyatt leaps on his cycle to ride off for help, but the truck has turned back, and this time the man with the gun takes deliberate aim and blasts Wyatt and his motorcycle off the road.