Rupert Pupkin is a delusional aspiring stand-up comedian trying to launch his career. After meeting Jerry Langford, a successful comedian and talk show host, Rupert believes his “big break” has finally come. He attempts to book a spot on Langford’s show, but is continually rebuffed by his staff and finally by Langford himself. Along the way, Rupert indulges in elaborate and obsessive fantasies in which he and Langford are colleagues and friends.
Hoping to impress, Rupert invites a date, Rita, to accompany him when he shows up uninvited at Langford’s country home. When Langford returns home to find Rupert and Rita settling in, he angrily tells them to leave. Rupert continues brushing off Jerry’s dismissals and Rita’s urging, until Jerry finally retorts that he had only told Rupert he could call him so Jerry would be rid of him. Bitterly vowing to work “50 times harder,” Rupert finally leaves.
Exhausted with rejection, Rupert hatches a kidnapping plot with the help of Masha, a fellow stalker similarly obsessed with Langford. As ransom, Rupert demands that he be given the opening spot on that evening’s episode of Langford’s show (guest hosted by Tony Randall), and that the show be broadcast in normal fashion. The network bosses, lawyers, and the FBI agree to his demands, with the understanding that Langford will be released once the show airs. Between the taping of the show and the broadcast, Masha has her “dream date” with Langford, who is taped to a chair in her parents’ Manhattan townhouse. Langford convinces her to untie him under the guise of seduction, and he seizes the gun to shoot Masha, but finds it was loaded with faulty pellets. He punches Masha in anger and flees downtown, where he seethingly sees Rupert’s full act on a series of television display sets.
Meanwhile, Rupert’s stand-up routine is well received by the audience. In his act, he describes his troubled upbringing while simultaneously laughing at his circumstances. Rupert closes by confessing to the studio audience that he kidnapped Langford in order to break into show business. The audience laughs, believing it to be part of his act. Rupert responds by saying, “Tomorrow you’ll know I wasn’t kidding and you’ll all think I’m crazy. But I figure it this way: better to be king for a night, than a schmuck for a lifetime.” Having shown the broadcast to Rita at her bar, he proudly submits to his arrest, as the FBI agents profess distaste for his jokes.
The movie closes with a news report of Rupert’s crime, his six-year prison sentence, and release after two years, set to a montage of storefronts stocking his “long-awaited” autobiography, King for a Night, stating that Rupert still considers Langford his friend and mentor, and that he is currently weighing several “attractive offers,” including comedy tours and a film adaptation of his memoirs. Rupert later takes the stage for a television special with a live audience, and an announcer enthusiastically introducing him repeatedly, while Rupert himself prepares to address his audience.