Best friends Enid and Rebecca face the summer after their high school graduation, with no plans for their future other than to find jobs and live together. The girls are cynical social outcasts, but Rebecca is more popular with boys than Enid. Enid’s diploma is withheld on the condition that she attend a remedial art class. Even though she is a talented artist, her art teacher, Roberta, believes that art must be socially meaningful and dismisses Enid’s sketches as nothing more than “light entertainment”.
The girls see a personal ad in which a lonely, middle-aged man named Seymour asks a woman he met recently to contact him. Enid makes a prank phone call to Seymour, pretending to be the woman and inviting him to meet her at a diner. The two girls and their friend, Josh, secretly watch Seymour at the diner and make fun of him. Enid soon begins to feel sympathy for Seymour, and they follow him to his apartment building. Later they find him selling vintage records in a garage sale. Enid buys an old blues album from him, and they become friends. She decides to try to find women for him to date.
Enid has meanwhile been attending her remedial art class, and she persuades Seymour to lend her an old poster depicting a grotesquely caricatured black man, which was once used as a promotional tool by Coon Chicken Inn, the fried chicken franchise now known as Cook’s Chicken, where Seymour works as a manager. Enid presents the poster in class as a social comment about racism, and Roberta is so impressed with the concept that she offers Enid a scholarship to an art college.
Seymour receives a phone call from Dana, the intended recipient of his personal ad. Enid encourages him to pursue a relationship with Dana, but she becomes unexpectedly jealous when he does so.
Enid and Rebecca’s lives start to diverge. While Enid has been spending time with Seymour, Rebecca starts working at a coffee shop. Enid gets a job at a movie theater so she can afford to rent an apartment with Rebecca, but her cynical attitude gets her fired on her first day. The girls argue, and Rebecca abandons the idea of living with Enid.
When Enid’s poster is displayed in an art show, school officials find it so offensive they force Roberta to give her a failing grade and revoke the scholarship. Enid turns to Seymour for solace, resulting in a drunken one-night stand. Seymour breaks up with Dana, and is called to account at work when the Coon Chicken poster is publicized in a local newspaper. He unsuccessfully tries to contact Enid, only for Rebecca to tell him about Enid’s prank phone call, describing the way they mocked him at the diner. Seymour is upset and goes to the convenience store where Josh works. Another customer ends up in a violent confrontation with Seymour, resulting in his being injured and hospitalized. Enid visits him in the hospital to apologize.
After everything that has occurred Enid gives in to her childhood fantasy of running away from home and disappearing. She has seen an old man, Norman, continually waiting at an out-of-service bus stop for a bus that will never come. Finally, as Enid watches from across the street, Norman boards an out-of-service bus. The next day, while Seymour discusses the summer’s events with his therapist, Enid returns to the bus stop and boards the out-of-service bus when it arrives. A post-credits scene, shows an alternate version of Seymour’s scene in the convenience store, in which he wins the fight and is not injured.