Over the top and fundamentally unbelievable, “Eagle Eye” is still close to being a very fun Hollywood action flick. But it earns a rap on the knuckles for chickening out in its final scenes.

The reunion of the star and director of last year’s fall sleeper, “Disturbia,” this new film goes much, much bigger, like a season of “24” with a quicker payoff. The hardware is hard, the body count is high, and the goal is a political wipe-out of unprecedented proportions.

The youthful hero is Jerry (Shia LaBeouf), who loses his twin brother in a mysterious accident and suddenly receives a large and rather incriminating shipment of bomb-making supplies.

A mysterious female voice on a cell phone — which is about to torment Jerry for the next couple of whirlwind days — informs him that the FBI is about to arrest him. If he doesn’t follow her orders, the consequences will be severe. Especially for him.

That’s enough to make a guy feel disturbia. And he has an opposite number: single mom Rachel (Michelle Monaghan) has been getting threatening calls, too. By obeying the dangerous instructions of the unseen voice, they take the story closer to a wild Washington, D.C., climax.

Monaghan is 10 years older than LaBeouf and looks it, which might be why there isn’t much romance indicated between the two characters. The script, from an idea dreamed up by Steven Spielberg and hammered into place by a bevy of screenwriters, sticks to nonstop action.

Director D.J. Caruso keeps it coming. Jerry’s escape from a government building is enjoyable, but the movie’s big number — a car-plane chase through a D.C. tunnel — is almost completely incomprehensible when it comes to the simple business of where things are at any given moment.

All of this, even the fun stuff, is dogged by the persistent sense that any of the voice’s instructions could result in instant death for Jerry and Rachel, which would sort of wreck the whole plan. By moving so quickly, the film gives you precious few moments to think about this.

Other actors are tossed around like bumper cars, including the smooth-browed Billy Bob Thornton as an FBI agent, and the equally smooth-browed Rosario Dawson as a military investigator. LaBeouf and Monaghan are both adept at urgently running through crowds, although LaBeouf — a likable actor — needs to develop more than his default slack-mouthed expression.

I can take a certain amount of implausibility, but the final couple of scenes are a cheat, a reversal of a cool ending that would have given the movie a bit of heft. But “Eagle Eye” doesn’t have the courage of its very minor convictions.