In the charming yet dilapidated town of Endora, Iowa, Gilbert Grape bears an immense weight on his shoulders, acting as the main provider for his younger brother, Arnie Grape. This responsibility is exacerbated by the lingering pain of losing their father 17 years ago, which has left their mother, Bonnie Grape, confined by her struggles with severe obesity. The annual Airstreamers' Club gathering approaches, and Gilbert finds himself torn between familial obligations and personal desires, especially when it comes to keeping a watchful eye on Arnie, who exhibits a reckless fascination for climbing local structures.
The quiet monotony of their lives is stirred with the arrival of Becky, a delightful young woman traveling with her grandmother. Unfortunately, their journey hits a snag when their vehicle breaks down, stranding them in Endora. As Gilbert and Becky begin to cultivate a connection, the complexities of his home life threaten to complicate their budding relationship. In his pursuit of a few stolen moments with Becky, Gilbert mistakenly leaves Arnie unattended in the bath, resulting in a dangerous situation that deepens Arnie's fears and incites anger from Gilbert’s family.
Tension rises as Arnie, seeking attention and validation, makes another attempt to scale the town's water tower, resulting in his arrest. His mother, who has remained secluded at home for over seven years, faces her fears and makes a humiliating appearance at the police station to fetch him. Meanwhile, a planned birthday celebration for Arnie goes awry, leading to the destruction of two cakes meant to honor him—one lovingly made by his sister, while the other succumbs to chaos brought on by Arnie's joyful spirit. Strained to his limits, Gilbert's frustrations culminate in a regrettable moment of violence, leaving him to grapple with guilt as he drives away from the chaos.
In Gilbert’s absence, Amy steps in to support Arnie as he struggles with aquaphobia, aided by Becky’s understanding guidance. While the siblings navigate the fallout of their family's struggles, Gilbert embarks on a journey of introspection, ultimately finding a path back to his family just in time for Arnie's 18th birthday. He seeks forgiveness from those he has hurt, striving to rebuild their strained bonds.
Tragedy strikes again when Bonnie finally attempts to leave her bedroom only to be found dead by Arnie. With the authorities unable to remove her body efficiently, Gilbert and his sisters decide to take action, leading to a desperate and dramatic conclusion where they burn the house down, taking Bonnie's body with it.
As the dust settles on this tragic chapter, Amy begins a new chapter in her life as a bakery manager in Des Moines, while Ellen prepares for fresh academic endeavors in a broader city. Meanwhile, Gilbert stands by the roadside with Arnie, both awaiting the return of their friends, Becky and her grandmother. As they look towards a future filled with infinite possibilities, Gilbert assures his brother, > "We can go anywhere."
