With his jock good looks, diffident air and squinty-eyed intensity, Matt Damon is an unlikely looking movie hero. But maybe that's why he's so good as ex-CIA hit man Jason Bourne in "The Bourne Supremacy," a movie in which not only the "hero" but the world around him is out of joint.

Almost as good as its predecessor--the Robert Ludlum-derived 2002 hit "The Bourne Identity"--"The Bourne Supremacy" is another brainy, fast spy thriller with another off-type lead by Damon. Reprising his role of Bourne, the deep cover agent trying to flee a killer's past and his own ruthless employers, Damon gives this whirling film an ultra-cool center.

Along with screenwriter Tony Gilroy and new director Paul Greengrass ("Bloody Sunday"), he keeps this intellectual roller coaster roaring and crashing along--without a wasted moment.

Whether or not you like this kind of genre movie, "Bourne Supremacy," like "Bourne Identity," is a close to perfect example of an expertly designed and executed thriller. Gilroy and Greengrass don't really adapt Ludlum's 1986 book--an archetypal bestseller rooted in the Cold War era--but they do preserve its themes, world-view and hectic, tightly knit pace. And they keep and extend the great basic idea: a hero who is a reluctant assassin, his memories wiped out, constantly pulled back into the deadly, amoral world he wants to escape.

Screenwriter Gilroy finds a way to continue the story past "Identity"--when Bourne and his girl-on-the-run Marie (Franka Potente) evaded or killed all their pursuers and settled down in what they hoped would be permanent anonymity. In Ludlum's original novel, Marie (a different Marie from the movie's) was kidnapped by Bourne's old CIA employers as part of a plot to enrage, then reactivate him as an assassin. Here, in the movie's somewhat analogous first scene, Bourne and Potente's Marie are pursued by malignant hit man Kirill (Karl Urban of "Lord of the Rings") with deadly results that send Bourne back into the rat race of international assassination.

Added to the mix is a series of mysterious hits that Bourne hasn't committed; Joan Allen as Pamela Landy, a new CIA operative (replacing "Identity's" heavy, Ted Conklin, played by Chris Cooper); Julia Stiles as operative Nicky, and more dirty work for Brian Cox as Conklin's ex-crony Ward Abbott.

That's as much as you need to know about the new movie's story; in any case, the slightly familiar plot elements act like a starter's gun, hurtling the characters and us into nonstop action. Perhaps that's what made the first movie so good: It was familiar enough in some ways to catch us off guard. The fact that it had plenty of the same spy-thriller conventions and cliches that have been teasing and pleasing us since the dawn of James Bond pushed us right into the action, while its surprises, humanity and storytelling constantly kept us on edge.

Greengrass, who replaced previous director and current "Supremacy" executive producer Doug Liman (because Liman was busy with "Mr. and Mrs. Smith"), doesn't miss a step. In "Bloody Sunday," Greengrass' mock-cinema verite bio-drama about the IRA confrontation and massacre, he generated an incredible sense of immediacy and danger--and that's what he does here, with far more improbable material. It's Greengrass' ability to convince us of the wildly implausible that meshes strongly with the movie's theme of humanity trapped within inhuman systems.

Damon, with his kid's face and ability to switch personalities, has a perfect character type here: a killer who looks like a kid. Damon was cheated of a potentially great role in the Anthony Minghella film of Patricia Highsmith's ice-cold classic "The Talented Mr. Ripley," when Minghella, curiously, decided to write and direct the title role as more vulnerable and overtly gay. That's not the way to play Ripley, as Alain Delon had already proven in Rene Clement's "Purple Noon."

But Damon, as the supposedly more sympathetic Jason Bourne, shows just how well he could have played Highsmith's true psychopath. And around him is a crack supporting cast. The precise, always-convincing Allen lends edge to what might have been a colorless antagonist's part. Urban, playing Kirill like an Olympic athlete of death, has blood-freezing moments. Cox, a great character actor at his peak in the past four years (in movies like "Troy," Adaptation" and "LIE"), here uses his jaded, world-weary face and air of cynical despair to mine something very near tragedy from Abbott.

But if the ensemble seems perfect, it's because the ideas are so strong--and because we know enough about movies like this to know how much extra everybody is putting in. The whole notion behind the first two "Bourne" novels and movies is a brilliant hook: identifying with a killer who's trying to run from his bloody nature, while fighting villains totally comfortable with theirs. With that hook, the dark world "Supremacy" paints becomes more and more real as we watch--and the world explodes.