Fear and Loathing in Las Vegas tells the story of Hunter S. Thompson's journey to Las Vegas in 1971 as a journalist for a sports magazine. Thompson is accompanied by his "attorney," a Samoan whose only counsel seems to consist of recommending drugs. Indeed, Thompson's assignment is only an excuse for the pair to rent a red Chevy convertible and scream off into the desert with a trunk full of illegal narcotics.

After picking up a hitchhiker who subsequently flees in response to their drug-induced hostility, Thompson and his attorney stop at the Mint Hotel. Thompson has been assigned to cover the Mint 400, a motorcycle and dune buggy race on the outskirts of the city. Despite some initial difficulty securing their reservation and attaining their press packets due to their inebriated state, they travel to the racetrack where the Mint 400 is to be held.

Unfortunately, the dust stirred up by the racers makes it nearly impossible to see what is happening or to ascertain a winner. Thompson departs the track with scant information for his story. In the meantime, he and his attorney have been running up a tremendous room service bill and carousing in the bars and casinos of Las Vegas. Drug abuse and sleep deprivation render the two deranged, particularly the attorney, who threatens Thompson with a knife in a sudden frenzy. Although the situation is diffused, soon thereafter the attorney departs Las Vegas for Los Angeles.

Thompson remains in Las Vegas for some time after his attorney leaves. As he becomes increasingly paranoid about being arrested or called to account for his room service bill, he decides to return to L.A. His flight is delayed by a telegram from his attorney telling him to stay put, because Thompson's been hired by Rolling Stone magazine to cover the National DA's seminar on illegal drugs. At first, fueled by anxiety, Thompson decides to leave Las Vegas anyway. He climbs into the Chevy and heads east, but when the California Highway Patrol stops him, he realizes that he is in no condition to drive himself to L.A. He also rethinks his decision to refuse the job covering the seminar. The twisted irony of a drug abuser mingling with cops and narcotics investigators is enough to make him turn back toward Las Vegas.

Arriving at his suite in the Hotel Flamingo, Thompson finds his attorney with a young runaway, Lucy. The girl, a would-be artist who draws portraits of Barbra Streisand, is clearly drugged. Thompson's attorney has taken advantage of her sexually during her semi-aware state. With some difficulty, Thompson convinces his attorney that Lucy is a liability, and the two drive her to another hotel-under the guise of taking her to a Barbra Streisand concert-and leave her there. Though Lucy later attempts to contact Thompson, she is brushed off and not heard from again.

The DA's conference is an unqualified waste of time. The only thing Thompson learns is that the investigators are ten years behind in their estimation of the extremity of the drug problem in America.

One morning, a maid enters their suite to find Thompson asleep and his attorney vomiting in the closet. After a brief altercation, Thompson and his attorney explain to the maid that they are narcotics investigators there for the seminar. Taking their fabrication one step further, they hire her as an undercover operative. The maid leaves with a promise not to tell anyone what she has seen.

Soon after the episode with the maid, Thompson drives his attorney to the airport. Thompson intends to remain in town longer, but over the next few days his actions start catching up with him. He realizes it's time to return to L.A. With the seminar over, cops and investigators have made a mass exodus to the airport. Embittered by his perception of the conference, he boards a plane and leaves, having pushed himself beyond fatigue and into a state of near-hysteria.