Bill Kincaid (Edward Norton), an up-and-coming philosophy professor, is called to his Oklahoma hometown following the alleged death of his twin brother Brady (Norton again). When he gets there, he finds Brady is alive and well. Brady concocted the story of his death in order to bring his brother to town to provide an alibi. Brady, a local pot grower, is being hassled by rival drug dealers, as well as local drug lord Pug Rothbaum (Richard Dreyfuss). Brady travels to the city and kills Rothbaum as Bill, masquerading as Brady, visits their hippie mother (Susan Sarandon) at the local rest home.
Unfortunately, as Brady and his friend case Rothbaum at the local synagogue, they are spotted by a dentist who flew into town with Bill. The dentist believes Bill killed Rothbaum, and goes hunting for him. He ends up shooting and killing Brady, and is shot by Bill. Brady takes the gun, to take the blame, as he dies.
Bill, trying to make amends, tries to sell Brady's pot garden to one of his rivals, in order to keep Brady's girlfriend and his unborn child safe. It does not go as planned, and Bill is shot in the back with a crossbow. His life is saved by Brady's best friend Bolger (Tim Blake Nelson).
At the end of the movie, Bill is seen recovering in Oklahoma with his family, Bolger, and his new girlfriend, Janet (Keri Russell)