A train. A bomb. A bomber. A mystery woman. And a ticking clock.

“Source Code,” the second film by “Moon” director and David Bowie offspring Duncan Jones, builds itself out of these classical Hitchcock-style elements. Through a computer virtual reality program, a military program places an injured air force captain onto a train outside of Chicago. After eight minutes, the scenario ends. He zaps back into a locked control room on a military base, only to be sent back to the train and repeat the exercise. His mission is to find the bomb and the bomber aboard the train – before it’s too late!

“The Groundhog Day meets” descriptions write themselves. But there is a more important similarity to notice – this quite engrossing film falls in line with the recent “dream movie” trend found in “Inception” and “Avatar.”

Cameron’s Marxist moonbeam masterpiece proves that there are no interesting philosophical premises that can’t be pushed aside for a CG dragon fight. Yet up to the second act, the film actually needles together an interesting theme, as the injured soldier Jake Sully wonders which is real and which is the dream – his material life as a paraplegic soldier or his computer-generated life as the tallest smurf.

“Avatar” and “Source Code” are early entries in a newborn and developing theme: the multiplicity of identity in the technological world. Why is this especially intriguing? If it ever feels like storytelling is merely repeating time-tested premises and themes, the rapid increase in technology is opening up new ideas and new ways of thinking. In past centuries, philosophers held this power. Now it’s the computer nerds. They may not be having any of the sex, but they are having all of the other fun.

There are a couple of other bombs in the movie, too. How exactly a score this terrible makes it into a movie directed by the son of one of the world’s most famous musicians, we’ll never know. The acting is all over the place. While mostly the actors play it dull and straight, Jeffrey Wright plays the program director like an audition for Lex Luthor. This would be more disturbing if not for Gyllenhaal, who seems to be shedding his damaging puppy dog image just as his box office popularity recedes. His hair isn’t yet graying, but it feels like it, and it works for a role that might have been played by Cary Grant in another day and age.

The film reaches a natural stopping point, it even stops there, and then it decides to keep going, seemingly for the purpose of achieving unlikely happiness. Aside from seeming cheap, it robs the film of its best premise. If we are all dwelling and dreaming inside a computer, then is there any way to achieve reverie and grace? Does the morality and fulfillment in the virtual world equal that of the material world? This is the question that “Source Code” approaches but never quite reaches.