(CNN) -- Prepare to be blown away -- again and again and again.
Yes, "Source Code" is that good. But it's also true in a literal sense: Being repeatedly blown away is part of the mission facing a disoriented and increasingly distressed U.S. Army officer named Colter Stevens (Jake Gyllenhaal) as he tries to find the terrorist who planted a bomb on a Chicago commuter train.
This is a most unusual suicide mission. For one thing, the bomb already went off, but Stevens is sent to relive the experience through a process that blurs the lines between ESP, time travel and quantum theory.
By tapping into the lingering short-term memory cells of one of the bomber's victims, scientists are able to "place" Stevens in the man's head -- and more than that, in his shoes -- for the eight minutes leading up to the blast. At the moment of death, Stevens re-emerges into what he thinks of as the real world, only to be sent back into the train with another eight minutes to fish out the killer.
The science is pure fantasy, the mother of McGuffins, but director Duncan Jones does his level best to keep us as off balance as his hero, whose grasp of the here and now seems to have been fried some time before the movie begins. At first he assumes he's in a training exercise, the Rolls Royce of role-playing simulations.
Yet it's too real, and too painful, for that. Each time he goes back into the train, the past becomes as malleable as the present -- except that as the timer ticks down, it always ends the same way.
Imagine a cross between "Groundhog Day" and "Murder on the Orient Express" and you're halfway there. Stevens has to negotiate his way through a set pattern of external events, including the conversation of the woman sitting across from him (Michelle Monaghan), and the progress of the conductor, while he tries to build up a mental dossier on each suspicious passenger in the crowded commuter car.
But Bill Murray wasn't blown to smithereens every eight minutes, and Ben Ripley's ingenious script isn't really a whodunit. That's the least satisfying aspect of the story, and only Stevens' disorientation excuses his poor deductive skills.
If you think of the film as a kind of recurring nightmare in the paranoid style of Philip K. Dick you're nearer the mark. Stevens' superiors (Vera Farmiga and Jeffrey Wright) try to keep him focused on their real world objectives, but he will keep drifting -- his fleeting connections with the doomed passengers somehow seem more important.
As authoritative an exercise in fractured storytelling as Christopher Nolan's "Memento," "Source Code" represents a real advance for Jones, whose only previous film was the micro-budget sci-fi "Moon."
Impressive as that was on a technical level, "Moon" felt as emotionally remote as its marooned hero. "Source Code" is an altogether richer and more accessible experience -- the existential popcorn flick that Gyllenhaal's "Donnie Darko" director Richard Kelly hasn't quite been able to pull off.
As for Gyllenhaal, he's more compelling here than he's been in a long time. There's a haunted quality about his desperate heroism that's cumulatively profound. Stevens knows he's stuck in a purgatorial loop with no end in sight, but every time the bomb goes off we can see that he dies a little.