Gilbert Grape is a small-town young man with a lot of responsibility. Chief among his concerns are his mother, who is so overweight that she can't leave the house, and his mentally impaired younger brother, Arnie, who has a knack for finding trouble. Settled into a job at a grocery store and an ongoing affair with local woman Betty Carver, Gilbert finally has his life shaken up by the free-spirited Becky.
Grocery store clerk Simon occasionally sells drugs from his cash register at work, so when soap opera actors Adam and Zack come looking for Ecstasy on a quiet Christmas Eve, they are surprised to find Ronna covering his shift. Desperate for money, Ronna decides to become an impromptu drug dealer, unaware that Adam and Zack are secretly working for obsessed narcotics officer Burke.