In the small town of Endora, Gilbert Grape (Johnny Depp) is busy caring for his mentally challenged brother Arnie (Leonardo DiCaprio) as they wait for the many tourists' trailers to pass through town during their yearly camp ritual at a nearby recreational area. His mother, Bonnie (Darlene Cates) is morbidly obese after years of depression following her husband's suicide. With Bonnie unable to care for them by herself, Gilbert has taken responsibility for repairing their shanty of farmhouse and looking after Arnie, who has a habit of climbing up the town water tower (like Spider-Man) if he is left unsupervised for too long, while his older sister Amy (Laura Harrington) and younger sister Ellen (Mary Kate Schellhardt) slave away in the kitchen. The relationship between the brothers is one of care and protection. In order to cope with his frenetic life, Gilbert has taken on a secret love affair with a housewife, Betty (Mary Steenburgen), whilst her insensitive, unsuspecting husband Ken (Kevin Tighe), is fully intent on selling Gilbert insurance for his family. A new chain supermarket has opened, threatening the small Lamson's Grocery store where Gilbert works, as well as threatening all the other small-time businesses in Endora. The chain supermarket stocks all kinds of goods, rendering many of the local shops redundant. This is a key theme in the film - which constantly portrays the futility of goods made with love in light of ever sweeping corporate greed.While the family prepares for Arnie's upcoming 18th birthday party, a young woman named Becky (Juliette Lewis) and her grandmother are stuck in town when their truck towing their trailer breaks down. Gilbert's unusual life circumstances threaten to get in the way of their budding romance. In order to spend time with Becky watching the sun set, Gilbert leaves Arnie alone in the bathtub by himself, believing he is now old enough to get out on his own. He returns home late and wakes up the following morning to find Arnie still in the bath, shivering in the now-cold water. Gilbert's guilt is compounded by his family's anger. As a result Arnie refuses to get near water, including the pond by Becky's trailer, and his fear causes him to become extremely dirty, adding to the many problems Gilbert faces. Betty's affair with Gilbert ends when she begins to make demands on him and tries to have sex with him while he's on the phone with her husband, Ken. Ken drowns after suffering a cardiac arrest and landing face down in his sons' wading pool. Many of the townspeople believe Betty killed her husband, despite the insistence of Gilbert's friend, Bobby McBurney (Crispin Glover), one of the town coroners, that believes it was a cardiac arrest. Besides Bobby, Gilbert is the only one who believed Betty didn't commit murder, and she eventually leaves town in search of a new life.Becky bonds with Gilbert and Arnie and helps Gilbert reflect on his feelings. They become deeply involved in conversation until Gilbert realizes that Arnie is missing. He has returned to the water tower he is forever trying to climb and this time has succeeded at getting to the top. Arnie is arrested, compelling Bonnie, who has not left the house in seven years, to rush to the police station to demand his release, causing her appearance to be ridiculed by the townspeople.Later at home, Arnie prematurely eats some of his birthday cake, which Gilbert told him not to touch. Gilbert orders Arnie to take a bath as punishment, and Arnie resists when Gilbert tries to force him. Losing his temper, Gilbert strikes Arnie-hard. Appalled at himself and angry at his life in general, Gilbert drives away, leaving Endora. Arnie leaves the house to find Becky, who takes care of him. Gilbert returns to town and sees Arnie with Becky, who is able to get him to enter the lake, and thus Arnie overcomes his fear of water. After Amy and Ellen come to Becky's and take Arnie home, Gilbert approaches Becky and the two talk about his own frustration and the reality of his father's death. The next day he returns home during Arnie's birthday party to apologize.