After releasing Moon, his first feature-length film, director Duncan Jones was able to write his own ticket to a certain extent. Moon had been a clever, perhaps even a little moving, picture with a smashing premise and it’d all been done with a bare minimum of cast, crew and budget. Clearly he had chops.

Though Jones had co-written Moon, he decided to follow up with something written by another, in this case Ben Ripley. Ripley had been toiling away to, by his own admission, little effect doing rewrites for horror movies that weren’t being made and the brightest spots on his resume were a couple of sequels to Species. Yet in 2007 he had written and sold a spec script that quickly became known as one of the best unproduced screenplays in Hollywood. Completely convinced Source Code would never be made, Ripley never stopped hoping. And then Jones came to call.

Source Code takes an enormous leap forward in terms of budget (Moon only cost $5 million to make), but despite what initially seems like a concomitant increase in scale, the movie remains intimate and human-sized. So on the one hand it might seem as though Jones had not demonstrated an affinity for “big” movies, while on the other he had shown he knows exactly how to elicit real emotions and conflicts from a small cast regardless of the overarching premise.

The film begins without preamble. A helicopter pilot for the US Army, Colter Stevens (Jake Gyllenhaal) wakes up on a train he’s never seen before, across from a woman who seems to know him as someone else. He has no idea why or how he got there and understands even less about Christina (Michelle Monaghan), who begins to suspect that Colter’s behavior isn’t a joke, but something more serious. But before any of this can be resolved, the train explodes and everyone on board is killed, Colter included.

But the story continues. Colter finds himself locked inside some sort of capsule, strapped into his pilot’s chair and unable to free himself. An Air Force captain named Goodwin — Vera Farmiga, doing a lot with a role that’s superficially very simple — communicates with Colter via a video screen. She won’t say where she is or how all of this is happening. She does, however, make Colter’s mission clear: he has eight minutes to discover the bomb that will destroy the train and pinpoint the bomber. And just like that, Colter is back in his substitute body, reliving the same eight minutes.

More is discovered, both about Colter’s freedom of action within this time capsule of sorts and about the nature of the program that has put him into the situation. All Colter can recall is flying a mission in Afghanistan and the rest is a blank. Working from inside the simulation, he learns more about the people controlling him and his own fate. It’s very exciting and intriguing and Gyllenhaal does excellent work as a man torn between doing his duty and doing what’s best for himself.

You would think Source Code would become boring and repetitive, given that most of the movie is occupied by those eight minutes being lived over and over again. What keeps it from being so — and, indeed, the film’s whole premise is predicated on this — are the infinite variations on those eight minutes Colter Stevens has. He can do literally anything a person in that situation can do, including getting off the train to escape the explosion, though ultimately he is reeled in at the end of his time to run the simulation again.

I hesitate to compare Source Code to something like Groundhog Day, especially since Source Code is in no way a comedy, but there are some structural similarities that are worth pointing out. Colter, during the course of his unrelenting repetition of those eight minutes, begins to learn not only the secrets of the train and the bombing, but also how to take advantage of the foreknowledge he possesses thanks to the process. In Groundhog Day, Bill Murray’s character floundered around without much purpose for quite a while, but eventually he turned the situation into something worthwhile both for the people around him and for himself. Source Code does much the same thing, though the potential for fiery death is around every corner.

None of this would work at all if the actors did not occupy their roles so well. I’ve already mentioned Farmiga’s excellent performance as Colter’s real-world controller, but I would be remiss if I didn’t talk about Gyllenhaal and Monaghan in depth. Gyllenhaal is one of those actors who doesn’t want to be pinned down by any one type of role, and if you look at his filmography you can definitely see that. Colter Stevens is a hero, yes, and Gyllenhaal has played heroes, but Colter is emotionally deep and full of conflicting impulses, and it takes a good actor to bring out those qualities of the script and make them real for the audience. Monaghan has probably the most traditional of roles, that of the woman in need of rescue, but she also does a credible job of bringing life to a well-written character. Monaghan’s Christina may start out as an innocent without any inkling of the terrible fate that’s about to befall her, but by the end of the film she’s shown grit and integrity and the willingness to do right by the man she thinks she knows, but doesn’t really know at all.

I suppose it wouldn’t be a Duncan Jones movie without some question of the nature of existence, and Source Code revels in that ambiguity. It has the rare quality of being a first-rate thriller while also raising serious philosophical and theoretical issues. The latter are not so thudding that they bring the story to a halt, but are inextricably woven into the forward motion of the tale. Ben Ripley’s script was deservedly praised during its four-year journey to the screen. It’s a terrific piece of work.