What's Eating Gilbert Grape

The film opens in the small town of Endora, Iowa, where Gilbert Grape (Johnny Depp) is busy caring for his mentally handicapped brother, Arnie (Leonardo DiCaprio) as they wait for the trailers to come drive through town (their "annual ritual"). His morbidly obese mother, Bonnie (Darlene Cates) has done little except eat since her husband's death, and longs only to see Arnie live to the age of eighteen. With Bonnie unable to care for the children by herself, Gilbert has taken responsibility for repairing their old farmhouse and looking after Arnie, who has a habit of climbing the town water tower if he is left unsupervised for too long, while his sisters Amy (Laura Harrington) and Ellen (Mary Kate Schellhardt) do the chores and the cooking. The relationship between the brothers is of both care and protection, as Gilbert continually enforces the "Nobody touches Arnie" policy. A new "FoodLand" supermarket has opened, threatening the small Lamson's Grocery store where Gilbert works. In addition, Gilbert is having an affair with a married woman, Betty Carver (Mary Steenburgen).

The family is looking forward to Arnie's eighteenth birthday. A young woman named Becky (Juliette Lewis) and her grandmother are stuck in town when their car pulling an Airstream 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 sunset, Gilbert leaves Arnie alone in the bath-tub to bathe himself. He returns home late and wakes up the following morning to find Arnie still in the bath, shivering in the now freezing cold water; his guilt is compounded by his family's anger. From then on Arnie refuses to touch any sort of water, including the pond by Becky's trailer, making him incredibly dirty all the time. Gilbert's affair with Mrs. Carver ends when she leaves town in search of a new life following her husband's death — he drowned in the kiddie pool after suffering a heart attack. Becky becomes close to both Gilbert and Arnie and as she talks to Gilbert she begins to unlock some buried hopes, dreams and happiness. They become so involved in one of their talks until Gilbert realizes that Arnie is no longer there with them, and has returned to the water tower he is forever trying to climb, and this time has succeeded and reached the very top. Arnie is arrested after being rescued from the top of the tower, causing his mother — who has not left the house in seven years — to become the object of pointing, laughing, photo-taking, and gawking from the townspeople as she goes to the police station, forcing Arnie's release.

Soon after, Arnie tries to run away yet again from his bath and fights Gilbert when he tries to get him into the tub. Out of frustration, and due to Arnie having disobeyed Gilbert by eating his birthday cake before the party, Gilbert finally snaps and repeatedly slaps Arnie across the cheek. Guilty and appalled at himself, Gilbert takes his old truck and drives away without another word. Arnie is extremely upset and hurt and he begins to cry. He also runs away, to Becky's, who takes care of him for the evening before he is picked up by his sisters. While he was at Becky's, he builds up the courage to jump into the pond, applauded by Becky, while Gilbert watches from a nearby bush, unseen by them. After some soul searching and help from Becky after Arnie has left, Gilbert returns home during Arnie's birthday party to apologize to his family, and shares a special apologetic moment with Arnie.

Following Arnie's eighteenth birthday party, Bonnie climbs the stairs to her bedroom for the first time since her husband committed suicide. While there, she confides in Gilbert that she thought he'd never come back, and begs him not to leave again. She also tells him that he is the most important person in her life, calling him her "Knight in shimmering armor." When he tries to correct her idiom, saying it's supposed to be shining armor, she corrects him saying "No, you shimmer, and you glow...", and that evening she passes away. Arnie later tries to wake her, at first thinking that she was just playing, but discovers she has died, and immediately runs outside, where he is comforted by Amy and Gilbert as they ask him what happened. The children, not wanting to let their mother become the joke of the town by having her corpse lifted from the house by a crane and helicopters, follow Gilbert's idea and empty the family home of all of their possessions and Gilbert sets it on fire. A year later, Gilbert narrates what has happened to his family after his mother's death (the daughters have moved away to new lives), as Gilbert and Arnie wait by the side of the road for Becky and the rest of the trailers to return. When they do, Gilbert and Arnie drive off into the sunset with Becky and her grandma.