Ignatius J. Reilly, an obese young man dressed in a hunting cap and other strange attire, waits for his mother, Irene, outside of a department store in New Orleans, Louisiana. Ignatius is a medieval scholar who despises the modern world. While Ignatius waits, a policeman—Patrolman Mancuso—approaches and tries to arrest him because he looks suspicious. Ignatius gets into a fight with Mancuso, and an old man, Claude Robichaux, tries to defend Ignatius. When Irene exits the shop, she screams at Patrolman Mancuso to arrest Claude—who she claims must have started things—and she and Ignatius escape. They hide in a nearby strip club called the Night of Joy, where they order beers. Ignatius and Irene strike up a conversation with the bar girl, Darlene, and a fashionable young man named Dorian Greene, until the proprietor, Lana Lee, returns and throws them out—Ignatius and Irene are not the sort of customers she wants in her bar. Irene is very drunk by this time, and as she tries to drive away, she crashes her car. Patrolman Mancuso, who is walking home, comes across the wreck and gives Irene a $1,000 fine.
At the police station, Claude Robichaux shares a cell with a black man named Burma Jones, who has been framed and arrested for stealing cashew nuts. Even though the police know that Jones is not guilty, he is kept in jail. Claude is sent home—the sergeant realizes that he was involved in a misunderstanding and blames Patrolman Mancuso. The sergeant decides that, from now on, Mancuso must wear a different fancy dress costume to work each day until he apprehends a genuinely suspicious character. Jones is released, too, but told that he must find a job or he will be arrested as a vagrant. Jones finds his way to the Night of Joy and miserably takes an advertised job as porter. Lana will pay him much less than minimum wage, but Jones cannot afford to turn the job down—besides, Lana says she will call the police on him if he tries to quit. Jones befriends Darlene, who tells him that she wants to become an exotic dancer.
Irene tells Ignatius that he must go out and find a job to help pay off her fine. Patrolman Mancuso visits Irene and comforts her—she is very upset about the car crash and the fact that Ignatius is unemployed, spends all his money at the movies, and does not help her around the house. Mancuso suggests that she come bowling with him and his aunt, Santa Battaglia, and Irene agrees. Meanwhile, Ignatius resentfully begins his job search. He eventually finds a position as a clerk in the office of a textile factory called Levy Pants. The office is run by a meek man named Mr. Gonzalez, and the boss, Mr. Levy, is never there. The only other employee is an elderly woman named Miss Trixie, who is desperate to retire. Mr. Levy and Mr. Gonzalez want her to retire, too, but Mr. Levy’s wife, Mrs. Levy, insists that her husband must keep Miss Trixie on because work keeps Miss Trixie vital. Ignatius takes to life in the office very well, though he always arrives late and throws all the papers he is supposed to file in the bin while Mr. Gonzalez is not looking. He secretly writes a rude letter to a client named Mr. Abelman, who has complained about Levy’s products, which Ignatius with Mr. Levy’s name rather than his own. He also begins to write a journal of his experiences in the workplace (alongside the book he is writing about the medieval period, which he hopes will be very influential). He hopes that the journal will annoy his ex-girlfriend, Myrna Minkoff, who is a progressive political activist living in New York.
Ignatius and Myrna often write to each another, and after a particularly offensive letter from Myrna which accuses Ignatius of being politically out of touch, Ignatius decides to organize a race riot at the Levy Pants factory. He knows that most of the employees in the factory are black and are paid below minimum wage. Ignatius tells the workers to bring weapons into work, and on the day of the protest tries to convince them to attack Mr. Gonzalez. The black workers are reluctant to do this, however, and Ignatius’s riot is a failure. Mr. Levy fires Ignatius when he hears what he has done. Mrs. Levy is not happy about this—she believes Ignatius is a “young idealist” and says that,] to pay for what he has done, Mr. Levy must bring Miss Trixie to the house so that Mrs. Levy can give her a makeover.
Meanwhile, at the Night of Joy, Jones looks for a way to sabotage Lana’s business. He has noticed that a young boy comes in every day, takes packages from Lana, and gives her money. Jones wonders what is going on and Lana secretly tells the boy, George, not to come anymore when Jones is present. Darlene pleads with Lana to allow her a chance to showcase her exotic dance routine, which she has practiced with her bird, a large cockatoo. As part of the act, the cockatoo will rip her clothes off. Jones senses an opportunity for sabotage here and encourages Lana to give Darlene a chance. Lana finally agrees but demands some changes after she has seen Darlene’s act. Lana says that Darlene’s act is too smutty and that, instead, she must dress as a “virgin-y Southern Belle.” Jones must dress as a plantation slave and work the door. When Lana goes out of the room, Jones peeks into a forbidden cabinet under the bar and finds the packages Lana gives to George. He writes the address of the club on one these packets.
Irene is enjoying her friendship with Santa and their new friend, Claude Robichaux, who met Santa by chance and remembered Irene from the incident with Ignatius in which he was arrested. Claude takes a fancy to Irene and Santa tries to set the pair up. The only obstacle, as far as Santa can see, is Ignatius, whom she feels is a waste of space. Santa wishes that Ignatius could be locked away and suggests that Irene put him in a mental institution. Patrolman Mancuso still has not arrested anyone and has been demoted—he now works in the bus station bathroom. Ignatius lends him The Consolation of Philosophy by Boethius to read, but one afternoon Mancuso tries to arrest George (who he has noticed with a suspicious package), and George escapes and steals the book from him. George gives the book to Lana because she has asked for school supplies for a project, which is seemingly related to the mysterious packages.
Ignatius goes out to look for another job and stumbles across a hot dog stand business called Paradise Vendors. He gets a job there but eats most of the hot dogs himself and does not make any money. The manager, Mr. Clyde, makes Ignatius wear a pirate costume and sends him into the French Quarter to attract tourists. One afternoon, in the French Quarter, Ignatius runs into Dorian Greene. He finds out that Dorian is openly gay, which gives Ignatius an idea for how he can involve himself in politics and annoy Myrna: he will form a political party of gay men, who will be so busy having sex with each other that they will not have time to go to war. Ignatius thinks he will bring about world peace this way. Dorian agrees to throw a party and Ignatius proudly heads home to write to Myrna about this.
George can no longer stash his packages from Lana in the bus station because Patrolman Mancuso is there, so he must find somewhere else to keep them. He decides to stash them in Ignatius’s hot dog cart, which Ignatius agrees to so long as George will watch the cart for him. Ignatius snatches one of the packages off George and discovers that there are pornographic photos inside. The woman in the pictures poses with school supplies (the same ones Lana requested from George) and Ignatius is amazed to see that her face is covered with a copy of The Consolation of Philosophy. He assumes that the woman must be a fellow intellectual and determines to track her down. As he passes the Night of Joy on his way home, he sees Jones at the door and asks him if any of the women who work there like to read. Jones says yes—he means Darlene, who reads magazines. Jones thinks that if Ignatius comes to the Night of Joy, he may cause trouble, which will sabotage Lana. He invites Ignatius to the opening night of Darlene’s show . Ignatius assumes Darlene is the woman who reads Boethius and agrees to come.
Ignatius attends Dorian’s party and finds that it is a wild gathering, attended exclusively by homosexual men. He tries to win them over with a speech about world peace, but this goes down very badly and Ignatius is thrown out of the party by three aggressive lesbians. Furious, Ignatius traipses down to the Night of Joy where Darlene’s opening night is about to start. Ignatius goes inside and takes a seat. When Darlene’s act starts, however, the cockatoo notices Ignatius’s earring—he is still in his pirate costume from work—and grabs ahold of it. Wrestling with the bird, Ignatius tumbles out into the street and is nearly hit by a bus before Jones pulls him back just in time. Ignatius faints, and a crowd, including several newspaper reporters, gathers around him. Lana Lee rushes outside and fires Jones and Darlene. A man in a silk suit approaches and Lana tries to sell him a pornographic photo. This man turns out to be Patrolman Mancuso, however, and he places Lana under arrest.
After Ignatius returns from hospital (having bumped his head when he fell), Mr. Levy arrives at his house and tells Ignatius that Mr. Abelman is suing him for a letter he believes Ignatius wrote. Ignatius denies that he wrote the letter and tells Mr. Levy that Miss Trixie is the one who wrote it because Mrs. Levy will not let her retire. Mr. Levy believes him and leaves. Irene, who is mortified that Ignatius appeared unconscious outside a stripe club in the newspaper, is sick of her son and calls up Santa for advice. Santa tells Irene that they must put Ignatius in the insane asylum—Irene is engaged to Claude now and must start a new life. Irene agrees and Santa calls for an ambulance to take Ignatius away. Irene does not want to see Ignatius taken away, so she rushes out of the house, saying a tearful goodbye to Ignatius as she leaves. Ignatius guesses what his mother has done and knows that he must escape, but does not know what to do. He is surprised by a knock at the door and is amazed to find Myrna on the doorstep. She has driven from New York to see him. Ignatius says that they must leave together at once, and he and Myrna escape just as the ambulance pulls into the driveway.
