Small-town auto mechanic Benny has devoted his life to caring for his schizophrenic sister, Joon, who isn't capable of living on her own. Her behavior drives away all of her caretakers, and Benny is informed by Dr. Garvey (Joon's psychiatrist) that it is time to consider placing her in a group home where she will be with her peers. The following day, Joon is picked up in the street by the police after Benny leaves her at home unattended to go to work. Benny brings Joon to his poker game, as he can't leave her alone. The days' events diminish Benny's sense that he can take care of Joon, and his friends later add to his dilemma by telling him about all the things he could be doing with his life if it weren't for Joon.

Meanwhile, Benny's friend Mike has his cinemaphile cousin Sam staying with him, and Joon sees Sam sitting in a tree. Joon talks her way into the poker game and "wins" Sam off Mike. Benny is at first outraged, but after an evening with Sam at the local diner (where Sam recognizes the waitress, Ruthie, from a horror film), and then coming home the next day to find Sam has cleaned the house, Benny decides Sam should be Joon's "housekeeper". While cleaning, Sam experiences one of Joon's "episodes", which results in Sam leaving, placing a present (a jack-in-the-box) for Joon on her doorstep, and waiting to be invited back - which Benny and Joon promptly do.

The next day, Joon aids Sam when he is struggling with writing to his mom, and the two go to the diner for tapioca. Ruthie takes them on errands, and then takes them home to an anxious Benny. After staying for dinner, Ruthie's car won't start and Benny drives her home, where they set a dinner date. Meanwhile, left alone, Joon and Sam almost kiss.

Later, Sam attempts to get a job at the video store, but is overwhelmed by the application. Benny and Ruthie have a fun date, but it ends abruptly. The next day, Benny, Joon and Sam go to a park, where Benny is down. Sam starts doing tricks, and a crowd gathers. Benny tries to persuade Sam that he could do more with his life than be Joon's housekeeper. Benny decides to stay at the park to reflect, and sends Joon home with Sam. When they arrive home, they make love, and Sam tells Joon he loves her.

Sam asks Benny the next morning how crazy Joon really is, and Benny changes the subject. While Sam gets his nerve up to verbally ask for a job at the video store, Benny persuades a buddy to let Sam audition. When Benny suggests to Sam that he should make something of himself, Joon becomes agitated and makes Sam explain that he and Joon are romantically involved. Benny throws Sam out of the house. Upset, he yells at Joon and shows her a pamphlet about the group home. Joon starts hitting Benny and screaming, but after he pushes her away she runs up the stairs. Feeling bad, Benny leaves to get her some tapioca. While he is away, Joon burns a childhood picture of them and sees Sam at the door. They get on a bus, as if to run away, but Joon begins to have an anxiety attack. Sam can`t deal with her behavior. The bus is stopped, and an ambulance arrives to restrain Joon. When Benny arrives at the hospital, Dr. Garvey tells him Joon doesn't want to see him. He finds Sam in the waiting room, and they argue. Sam goes to stay at Ruthie's, who rents apartments.

Benny finds Sam at the video store and asks for his help. They go to the hospital. Benny persuades Joon to consider getting her own apartment and tries to convince her that Sam has come back for her. While being interviewed by Dr. Garvey, Joon sees Sam swinging on a rope outside her window and waving, and she states that she would like to try living in her own apartment. Dr. Garvey agrees to try out her choice, but Sam's rope breaks, and he breaks his ankle. Benny and Joon reconcile, and Sam and Joon are reunited upon her release.

At the end, Benny brings roses to Ruthie. He takes another bouquet upstairs to Joon's apartment but smiles and leaves the flowers in the doorway when he discovers Sam and Joon together contentedly making grilled cheese sandwiches on the ironing board.

Aidan Quinn was brought in at the last minute to replace Woody Harrelson.

Considered a modest hit, grossing $23,202,734.

Rotten Tomatoes gave the film a rating of 72% positive based on 29 reviews.