Soldier Colter Stevens (Jake Gyllenhaal of DONNIE DARKO) awakens to find himself on a passenger train heading into Chicago. The woman he's sitting across from, Christina (Michelle Monaghan) seems to know him and calls him by a different name. When he gets up and looks in the bathroom mirror he sees a stranger--the guy doesn't look like him at all. Somehow, Colter's mind is in this guy's body. Then, the train explodes and he finds himself, back in his own flesh, in some type of capsule--and there's a woman, Goodwin (Vera Famiga of THE ORPHAN) speaking to him on a monitor. She, and a scientist/inventor Dr. Rutledge, eventually explain that he's on a mission to find out who planted and exploded the bomb because they think there will be a larger target that same day--the city of Chicago.
It's all sort of like GROUNDHOG DAY in that Colter has to keep reliving the same eight minutes in the past. Things get interesting, however, when he attempts to change history, something Rutledge insists would never happen since he's experiencing a sort of temporary reality in which he can only view the past. His going back those eight minutes is only sort of a copy of that event that exists for only those eight minutes. However, there are some twists and turns that make this all very interesting. Least to say, SOURCE CODE is one of the more satisfying time-travels in recent memory.