I'm really, really excited about Duncan Jones now. I was impressed by his soulful debut picture Moon. Source Code, to me, proves that he is more than a one-hit wonder and is capable of consistently intelligent filmmaking and I look forward to his next film.
I have to admit though, I thought the title was misused. Source Code to me suggests a way of re-writing the program underlying existence itself - as in the Matrix, or perhaps Greg Bear's novels where quantum reality turns out to have computational properties. Source Code here is just a cool codename for a time-travel project. The trailer was misleading too - speeding trains, running plus explosions in trailer language translates as action-thriller with superhuman stunts. While there is certainly action, it's on a much more human and believable level and the film is more of a postmodern whodunnit with (naturally) existential twists.
Jake Gyllenhall plays a soldier, Stevens, sent back in time into the mind of a passenger on a doomed train, in order to work out the identity of the bomber. He can't avert the crisis which has already happened but the hope is to stop a second, larger attack.
Stevens can be sent back repeatedly, replaying the scenario in different ways - but if this is another Groundhog Day it is a particularly viscious one in which Stevens dies violently at the end of each iteration. The plot also reminded me of a short-lived time travel series, Seven Days, which also featured an experimental team led by a paraplegic scientist (here played by Jeffrey Wright.)
Source Code's plot relies on a particular version of time travel theory and the scriptwriter understands the implications and paradoxes, something missing from Seven Days. It's well-written drama too: the exchanges between Gyllenhall trapped in his capsule between sorties, and his commander Goodwin (Vera Farmiga) are particularly emotional. While the film gives up some of its secrets slightly too easily, the overall plot develops in ways that are captivating and surprising.