Commuters, you know the drill.

You jolt awake on the train; the woman in the facing seat is talking to you but addressing you by someone else's name.

Deal with that later. Right now, you have this sickening premonition that you have to save the world and that time is most emphatically not on your side.

Never experienced that on the 7:42 a.m. express into the city? Well, it happens to Jake Gyllenhaal's character in the choppy thriller Source Code. Over and over and over again.

What the deuce is going on? The last thing you knew you were a combat pilot on a mission over Afghanistan. Now you seem to be a civilian, repeatedly revisiting this urgent scenario like you're stuck in some kind of truncated Groundhog Day.

Luckily, the brief span you are given - precisely eight minutes - proves to be remarkably elastic. It can go by in a flash or it can take up the whole last reel of the film.

In between trips on the cuckoo choochoo, you are yourself again: Capt. Colter Stevens. But harnessed in some isolated cargo hold. On a small screen, your handlers, with growing frustration, are trying to get you to focus on the task at hand.

You're trying to follow the instructions of an Air Force officer with kind eyes (Vera Farmiga) and a blustery scientist (Jeffrey Wright). You know that he's brilliant because he hobbles around with a forearm crutch.

But why are they spoon-feeding you information? Why not just tell you what to do on the train and how to do it, rather than have you stumble through it time and again?

Meanwhile, you're sort of falling for that cute woman (Michelle Monaghan) on the train, the one who keeps calling you Sean.

Great, now you have to find and disarm a sophisticated device, identify and subdue the bomber, and get the girl. Ticktock, buddy. The clock is running.

Source Code certainly gives the audience a lot to chew on. But very little of it is digestible.

The quantum physics premise doesn't make sense, the villain is neither convincing nor creepy, the incremental narrative quickly grows tedious, and the film has all the continuity of Gary Busey on meth.

Gyllenhaal is particularly unsuited to this role, his saucer eyes flashing from calm to crazed. For most of the film, he resembles a horse that has just smelled smoke in the adjoining stall.

It doesn't help that the recurring calamity Gyllenhaal keeps failing to forestall looks so chintzy. Or that the dialogue is so clunky.

"How much time does he have?" asks a frantic Farmiga. "Some," mutters Wright darkly, "but not a lot."

Why beat around the bush? It's eight minutes. He always has eight minutes.

Contact staff writer David Hiltbrand at 215-854-4552 or dhiltbrand@phillynews.com. Read his pop-culture blog at http://www.philly.com/philly/blogs/dave_on_demand.