Shy, socially inept teenager Nick Twisp lives with his mother, Estelle, and her boyfriend, Jerry, in Oakland, California. When Jerry owes money to a group of sailors, he takes Estelle and Nick to a trailer park in Clearlake where Nick meets Sheeni Saunders, a bright young woman his age, with an interest in French culture and who shares Nick's musical taste. Despite Sheeni's boyfriend, Trent Preston, they become romantically involved. Nick purchases a dog for Sheeni named Albert (after Albert Camus), but the dog rips up the family Bible and Sheeni's parents ban it from the house.
Jerry needs to return to Oakland and takes Estelle and Nick with him. Sheeni promises to arrange a job in Ukiah for Nick's father, George, while Nick will get his mother to kick him out so he can return to Sheeni. Back at home, Nick creates an alter-ego named Fran ois Dillinger, a suave, rebellious troublemaker. Immediately after Nick makes the decision, Jerry dies of a heart attack. Under Fran ois' influence, Nick mouths off to his mom and her new boyfriend, police officer Lance Wescott. Nick takes Jerry's Lincoln, and crashes into a restaurant, which starts a fire. Lance agrees to lie and report the car stolen. In return, Nick must live with his father. In Ukiah, Nick phones Sheeni and tells her he had to blow up "half of Berkeley" to return. Sheeni's parents overhear this and ship her to a French boarding school in Santa Cruz, forbidding Nick ever to see her again.
In his new high school, Nick befriends Vijay Joshi, and they take Vijay's grandmother's car to visit Sheeni. After being allowed into Sheeni's room, Nick goes to the restroom and meets Bernice Lynch, Sheeni's neighbor, and claims Trent said terrible things about her. Bernice brings the matron to Sheeni's room and the boys flee. On the way home, the car dies and Nick calls Mr. Ferguson, his father's idealist neighbor, to come pick them up; he tells Ferguson that Vijay is an illegal immigrant whom Nick is trying to "free from persecution".
When he returns home, Nick meets Sheeni's older brother, Paul, who tells him that she will be returning home on Thanksgiving and invites him for dinner. Nick begins to send Bernice letters asking her to slip sedatives into Sheeni's drinks to make her fall asleep in class, thereby getting Sheeni expelled. Nick finds Lacey, George's 25-year-old girlfriend, Paul, and Ferguson, lounging in his living room, high on mushrooms, which Nick also ingests. George finds them and punches Ferguson, which results in Paul punching George. Lacey leaves the house to live with Paul. On Thanksgiving Day, Nick receives a call from his mother explaining Lance left and will not cover for Nick anymore. Nick goes to Thanksgiving at Sheeni's. Trent unexpectedly arrives and explains Nick's letters to Bernice; Sheeni is horrified and Nick leaves.
Nick steals his father's car to escape the police. He then removes his clothes and drives the car into a shallow lake in front of the police station. He buys a wig and a dress and impersonates one of Sheeni's "friends". He fools Mr. and Mrs. Saunders and goes up to Sheeni's room. Upstairs, Nick tells Sheeni that he understands what loneliness is like, and that everything he has done, including burning down Berkeley, destroying his parents' cars and having her sedated were all so that they wouldn't have to be alone anymore. Sheeni forgives Nick, and the two have sex, finally achieving Nick's dream of losing his virginity. Trent barges in, telling Nick he's brought the police with him. Nick beats up Trent and asks Sheeni to wait for him; Sheeni reassures him that he will only be in juvenile detention for three months.
The animated closing credits show Nick in jail with Fran ois helping him. When Nick is released, Sheeni shows up in a car and they drive away into the sky towards the Paris skyline, as various characters appear to make amends with the two and give them their blessing.
Output: Why is Sheeni's dog banned from the house?