July 28, 1999 | If you can see only one movie this summer about giant sharks with genetically re-engineered brains -- make sure it's Deep Blue Sea.

Of course, you might well ask yourself: Why on earth would anyone want to genetically re-engineer shark brains in the first place? Dr. Susan McAlester (Saffron Burrows) performs this miracle of modern science -- in flagrant violation of about five or six international treaties -- in the hope of producing a cure for Alzheimer's disease. Unfortunately, her ends don't entirely justify her means. By tinkering with the gray cells of three 40-foot makos in her control group, she inadvertently creates -- well, very smart sharks. Which, she quickly learns, is a very dumb thing to do. "You've taken God's oldest killing machine," a disapproving onlooker notes, "and given it will and desire."

Deep Blue Sea takes one of Hollywood's oldest horror-movie plots -- bad things happen when you mess with Mother Nature -- and gives it some fiendishly clever twists. The opening sequence takes a knowing wink at the prologue of Jaws, Steven Spielberg's famous fish story, then springs a genuinely surprising twist. Much later, the movie playfully acknowledges a genre convention -- there's a certain type of character who's always killed in this type of movie -- then defiantly breaks the rules. Somewhere in between, there's a much bigger shock, but it wouldn't be fair to even hint at what happens. Suffice it to say that, during one predictably unpredictable feeding frenzy, you're likely to exclaim: "I can't believe they did that!"

Here and elsewhere in Deep Blue Sea, director Renny Harlin (Cliffhanger) does a nifty job of making the movie move faster than a famished mako. That isn't quite fast enough to keep you from noticing the thinness of the characters or the contrivances of the storyline. But once Harlin finishes the heavy lifting of the long exposition, he infuses this hokey B-movie nonsense with more than enough urgency and excitement.

This is not what you might call an actor's picture, but Samuel L. Jackson is impressively authoritative as millionaire Russell Franklin, the financial backer of Dr. McAlester's weird science. Worried about bad publicity -- and, worse, plummeting stock prices -- when an enhanced shark briefly goes AWOL, Franklin threatens to pull the plug on Dr. McAlester's Acquatica Research Center, a decommissioned naval submarine base floating off the Pacific coast. So the good doctor invites her benefactor to Acquatica, to demonstrate the progress of her research. Naturally, nothing good comes of this.

With a little help from a taciturn shark wrangler (Thomas Jane), a know-it-all engineer (Michael Rapaport), and two eminently disposable fellow researchers (Stellan Skarsgard, Jacqueline McKenzie), Dr. McAlester puts on quite a show in her underwater laboratory as she uses brain matter from a mako to revitalize human tissue. Unfortunately, the mako makes its displeasure known by sinking its teeth into a not-entirely-innocent bystander. Even more unfortunately, the research center is badly damaged by a raging tropical storm and a helicopter mishap. As the human survivors scramble to reach the surface, the sharks swim into the sinking facility and stalk their prey through flooded hallways and waterlogged elevator shafts.

And remember, these are smart sharks. So smart, in fact, that when the comic-relief cook played by rapper-actor LL Cool J seeks refuge inside an immense oven, one of the brainy beasts knows enough to turn on the gas.

With a world-class team of f/x experts at his disposal, Harlin is able to keep his killer sharks in plain sight for long stretches of Deep Blue Sea. Even so, he's admirably restrained when it comes to dwelling on the dining habits of his big, bad beasts -- there is blood and carnage, of course, but not nearly as much as you might expect. And he's genuinely clever when it comes to devising scenes that scream "Boo!" -- or "Chomp!" -- when you're not quite ready for the frisson.

It should be noted, by the way, that at least one special effect has nothing to do with computer-generated makos. According to the production notes, Harlin and his producers deliberately cast talented non-stars in most of the lead roles, to keep the audience from easily guessing what characters would or would not survive. They claim their chief inspiration for this stratagem was the original Alien, a movie that subverted genre conventions by allowing a relative newcomer, Sigourney Weaver, to outlast her better-known co-stars. So it's quite possible that, when Harlin contrives to have Saffron Burrows (last seen kicking ass and taking names in Wing Commander) strip down to her underwear during an especially tense scene, he's paying homage to a similar unveiling of Weaver in the 1979 sci-fi classic. That, or he just wanted to showcase his leading lady in her bra and panties.