On the night of the discovery of a duplicate planet in the solar system, an ambitious young student and an accomplished composer cross paths in a tragic accident.
Rhoda Williams (Brit Marling), an astrophysics student at MIT, is driving when she sees a planet and leans out for a closer look. She hits a minivan and kills a family. She is imprisoned for four years, and upon release seeks out the widower of the family, composer John Burroughs (William Mapother). The planet she saw is a mirror planet of Earth, and an essay contest is held where the winner can ride a space shuttle to visit it. Williams considers the possibility of visiting it to find out what kind of life her mirror self would have led.