So what exactly is the source code? As one character relates, “it would take weeks to explain,” and time is something in short supply in this movie. On a morning commuter train traveling into Chicago, Capt. Colter Stevens (Jake Gyllenhaal) jolts up from a little snooze to find he doesn’t know where he is. His seatmate, Christina (Michelle Monaghan), keeps calling him Sean and his reflection in the train’s window reveals a different face.