We never learn much about the freelancers. Sam (Robert DeNiro) is American, ex-CIA -- or is he? Seamus (Jonathan Pryce) and Dierdre (Natascha McElhone, from The Truman Show and The Devil's Own) work for the mysterious Irish group. Gregor (Stellan Skarsgård, from Good Will Hunting and Amistad) is German, ex-KGB. Larry (Skipp Sudduth), another American, is a weapons-and-vehicles expert. We never know more than the nationalities of the Frenchman Vincent (Jean Reno) and the Englishman Spence (Sean Bean, playing wonderfully against the type he's made for himself as a terrorist heavy in movies like Patriot Games).

But in the hands of good actors -- and this cast is stellar -- a script that leaves characters undefined is no problem, because it's obvious that although the audience may know little about these characters, the actors portraying them have given a great deal of thought to who they are and where they come from. Small things like a sidelong glance or a twist in the delivery of a line ground these characters in real life, making the audience forget that these are actors working from a script and allowing us to feel as if these are genuine, solid people.

It's difficult for an action movie to shock anymore -- how many times can one see a car explode and be startled? But Ronin shocks with the blatant, unrepentant, and very public violence of this group of very secretive people. As the freelancers plan their ambush on the Russian motorcade carrying the suitcase, we see only their simple diagrams of the intersection where they'll launch their assault -- they plan diversionary explosions and massive gunfire. But as the Russian cars come to a stop at a traffic light in bustling downtown Nice and our operatives pop up left and right with guns, you realize with a start that this is where they had been planning their mayhem all along, with complete disregard for the many, many bystanders caught in the crossfire -- and even more daring, with an utter lack of concern for the local constabulary.

You might say that many action movies, on the surface, show the same lack of caring for innocent victims, but again it's the fabulous cast that makes Ronin something more. The businesslike attitude demonstrated during their advanced planning of the ambush, for example, makes their actions all the more disturbing.

A real filmmaker behind the camera is a huge bonus, too. The imprint of director John Frankenheimer (The Manchurian Candidate) is indelible upon Ronin. He has staged some of the most thrilling car chases ever filmed -- through narrow, narrow European streets barely the width of a single car, and through wrong-way traffic. And unlike most action movies, which linger for almost humorous asides as the innocent bystanders begin to survey the damage left in a chase's wake, throwing up their hands and scratching their heads, Frankenheimer's camera never stops moving, stays with the chase, leaving the victims to their own devices.

A nice director's touch: the film is gorgeously grainy, lending a feel of the age and grittiness of the story's settings, Paris and Nice. (You don't think Nice could be grimy? It's not all beaches and sidewalk cafés.) You can practically reach out and touch every crumbling building and feel every rain-soaked cobblestone beneath your feet.

Ronin is one not to miss.