In the opening scene of Source Code, Duncan Jones the director, has decided to include many camera angles and shots of a major city which I believe to be Chicago. The camera cuts many times from the city to a train, indicating to the audience that this train has a part in the film. A final frame of a river leads into a white light and then a close up of Jake Gyllenhaal character Colter Stevens. However, the storyline becomes a bit complicated after the close up. The first complication is that the women opposite him calls him Shaun. The next thing is that Colter Stevens keeps on looking around anxiously, this creates a lot of tension and suspicion around why he acts this way. Furthermore he acts out of character to what the lady across him is saying and then she become suspicious of him. All these sequences lead to an explosion and everyone dies. Then Colters Stevens awakes in a room.
This is very confusing and very complicated but the duration of the film makes everything clear. The plot of the film is that Colter Stevens must stop the train from blowing up and find out who blows it up. But he is dead and so his brain is what does it through a machine which is keeping him alive. The ending of the film is that everyone is safe and Colter Stevens saves everyone. Due to the machine changing the past, people wont know he has saved everyone and so he asks the people controlling his brain to send him back. This time he does everything he has to and more, he sends messages to people in the past and tells them the project was a success so that he could be remembered.
The remainder of the film isn't as good as the beginning of the film as it doesn't create suspense and tension for the audience and it doesn't raise as many questions as the beginning of the film does.