U.S. Army pilot Captain Colter Stevens (Jake Gyllenhaal), last aware of being on a mission in Afghanistan, wakes up on a commuter train to Chicago, at 7:40 am. To the world around him â including his traveling partner Christina Warren (Michelle Monaghan) and the bathroom mirror â he appears to be Sean Fentress, a school teacher. As he comes to grips with this revelation, the train explodes, killing everyone aboard.
Stevens regains consciousness inside a dingy dim cockpit, leaking oil. Communicating through a video screen, Air Force Captain Colleen Goodwin (Vera Farmiga) verifies Stevens' identity, and insists he stay "on mission" to find the bomber before a large "dirty bomb" hits downtown Chicago in six hours. Inside the "Source Code" experimental device designed by scientist Dr. Rutledge (Jeffrey Wright), he experiences the last eight minutes of another compatible person's life within an alternative timeline.