The story takes place in the small, rural town of Peacock, Nebraska, where we are introduced to central characters: a bank clerk named John Skillpa (Cillian Murphy) and his "wife", Emma Skillpa. One morning, Emma is doing laundry outside when the caboose of a train runs off the tracks and ends up in John's backyard. The community rushes to Emma's aid, and the woman rushes back into the house.
Meanwhile, it is election season and there are two candidates running for mayor. The conflict arises when Emma is asked by the wife of John's boss, Fanny Crill (Susan Sarandon), and political advisor Connor Black to host a political rally with the caboose of the train as a background. Emma agrees, while John is vehemently against the rally and is working to get the train removed as soon as possible. Similarly, John is also trying to help Maggie Bailey (Ellen Page) and her son leave Peacock, while Emma is trying to provide alternatives so that she can stay here. The film then goes back and forth between John and Emma, and their actions conflict with each other more and more as the film progress.
And the big issue tying all of this together? John and Emma are the same person, but are unaware of each others' actions.
This movie provides examples of:
- Bittersweet Ending: Emma entirely takes over as the dominant personality against John's will, and fakes John's death by killing a man. She intends to repeat the cycle of abuse with Jake, but realizes what she's become, and retreats back into isolation.
- Faking the Dead: Emma decides to kill off "John", and completely takes over as the dominant personality.
- Heroic BSoD: John has one because of Emma's meddling. Emma has one at the end of the film, when she realizes she's turned into just as much a monster as John's mother.
- Missing Mom: John's mom passed away a year prior to the movie, and people assume that John's isolation and awkwardness is because of this.