The couple that slays together stays together.

That's the heartwarming message conveyed in "Mr. and Mrs. Smith," a movie that does to Brad Pitt and Angelina Jolie what "Gigli" did to Ben Affleck and Jennifer Lopez.

In other words, it's the latest example of a dubious cinematic genre in which a tabloid-worthy glamour couple demonstrates how notorious off-screen sizzle can fizzle when caught on film by someone other than a paparazzo.

It's also the latest example of a lamentable trend in which a clever, quirky director -- in this case, Doug Liman -- falls victim to blockbuster bombast.

For now, however, let's consider the curious case of "Mr. and Mrs. Smith," a movie in which virtually no one -- not Pitt and Jolie, not Liman, not its five credited producers and certainly not screenwriter Simon Kinberg -- has the slightest concept of how to get where they seem to want to go.

Where they want to go is that magical realm of make-believe, where seeing's believing and audiences don't care that what they're seeing could never be true. But it's rarefied air up there, and not too many movies can breathe it without getting light-headed. "Mr. and Mrs. Smith" certainly isn't one of them.

It's so light-headed it faints dead away at regular intervals, for extended periods of time. And even when it's conscious, there's nothing on its mind -- because it doesn't have one. Even more disastrously, it doesn't have a heart.

Moviegoers are willing to forgive a lot -- too much, in most cases -- provided a movie gives them some reason to care, which is something "Mr. and Mrs. Smith" never manages to achieve.

How could it, when the title characters can't be bothered to care about themselves -- or each other?

The movie's premise -- two top assassins masquerading as a placid suburban couple -- may be far-fetched. But it also has great potential as a dark comic metaphor for a modern marriage so soulless that only killing -- and the strangely exhilarating notion of killing each other -- can bring it back to life.

Realizing that potential would require both smarts and heart. Instead, "Mr. and Mrs. Smith" seems caught up in the same problem its title characters share: a total indifference to anything except gleaming surfaces.

John and Jane -- not necessarily their real names -- have an outwardly ideal life, one that looks like they ordered it from a glossy catalog, complete with a perfectly appointed, perfectly manicured house on a street that might be just around the corner from TV's Wisteria Lane.

But Jane is far from a desperate housewife. She's a top assassin for a shadowy agency, who dispatches targets for six-figure fees. Just like her husband, whose prosperous engineering firm masks a lucrative extermination enterprise.

Neither of them knows -- or cares -- what the other does for a living. That is, until they find themselves on the same assignment, after the same target -- and in each other's gun sights.

From there, you might think "Mr. and Mrs. Smith" could be headed for the same hallowed ground Alfred Hitchcock tended so faithfully for so long: the intersection of love and danger, where made-for-each-other couples discover their love while running for their lives.

But abandon hope all ye who enter here. Screenwriter Kinberg ("XXX: State of the Union") displays no ability to create characters deeper than cardboard cutouts. (Except for one: Pitt's laughably neurotic partner Eddie, played by the dependably droll Vince Vaughn, who lives with his mother because "she's the only woman I've ever trusted." If only "Mr. and Mrs. Smith" had been about him and his romantic problems, it might have been worth watching.)

Likewise, Kinberg displays absolutely no flair for repartee, witty or otherwise. And because he also shows no grasp of logical plot construction, "Mr. and Mrs. Smith" is totally devoid of suspense. Watching it, you feel as though you're trapped in one of those mindless, endless video games, with explosions and car chases and hand-to-hand combat confrontations playing in an endless loop.

Director Liman knows better, of course -- and has done better, too, whether in independent hits ("Swingers" and "Go") or a mainstream winner like "The Bourne Identity," all of which benefit from his imaginative eye and offbeat sensibility.

Here, Liman proves he can stage soulless bombast with the best (or worst) of them. It's a dubious achievement, made even more disheartening because of the movie's flip, lighthearted and utterly casual approach to deadly violence.

When Mr. and Mrs. Smith confess to each other that they never have any trouble sleeping after a hit, it's hardly a surprise -- these are characters who can't get turned on unless they're stalking each other, guns drawn, or battling until they're bruised and bleeding. No wonder they need a marriage counselor.

And no wonder Pitt and Jolie never generate any genuine chemistry. Unless they're fighting, their characters never get together. And even when they do, they're too busy posing and preening to seem like anything other than models demonstrating the latest in chic spywear and high-tech espionage equipment.

But maybe that's the point. Maybe "Mr. and Mrs. Smith" is really as soulless and shallow as its plastic protagonists.

Or maybe I just need to dig out my "Prizzi's Honor" video to remind myself that great movies about contract killers in love do exist. But they're not called "Mr. and Mrs. Smith."