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Toward the close of the new horror thriller “Saw,” about a mysterious serial killer who tortures his victims by putting them into gruesome traps that they must quickly escape–usually by doing severe damage to themselves or others–or die, some of the characters are running around in an underground tunnel, and a sign appears prominently reading “Caution–Raw Sewage.” At another point, one of the cops trying to track down the madman says to his partner, as they search in a nice area of town, “The sewer lines run under this neighborhood, too.” A good many viewers will probably think the theme of untreated waste particularly appropriate; “Saw” is a movie that will repel lots of people with its gleefully misogynist attitude, its ghoulish sense of humor and its abundant gore. On the other hand, the picture will undoubtedly attract a cult following for those very same attributes. You should be able to determine pretty easily which of the two groups you’ll fall into.

“Saw,” made on a minuscule budget by a couple of Australian film-school graduates, is a shocker that combines the puzzle-like format of “The Usual Suspects” with the grim police procedural mode of “Se7en.” (It wouldn’t be far afield to call it “The Usual Se7en.”) It opens in a filthy, abandoned underground bathroom, where a doctor named Gordon (Cary Elwes) and a slacker photographer called Adam (Leigh Whannell, who also scripted) wake up chained at opposite ends of the room. A dead body lies between them in a pool of blood, an apparent suicide; the gun is still in his hand. A tape recording, retrieved with some difficulty, orders Gordon to kill Adam, or their abductor will kill the doctor’s wife (Monica Potter) and young daughter (Makenzie Vega), who are also his prisoners.

This opening segment of the picture is an exercise in talky desperation, dribbling out information in a fashion not unlike the conversation between Kevin Spacey and Chazz Palminteri in “Suspects.” But the picture soon leaves the captives behind to show, quite out of chronological sequence, the search for a serial killer called “The Jigsaw”–obviously their abductor–by a couple of cops (Danny Glover and Ken Leung), the older of whom becomes increasingly obsessed with catching the gruesomely inventive mastermind. The structure is deliberately fractured and disorienting, jumping back and forth from the past police investigation (in which Dr. Gordon himself became a suspect at one point) to the two men in the basement, trying desperately to find a way out of their common problem while getting to know one another, to the predicament of Gordon’s family. (The title comes from the fact that Gordon is provided with a saw with which he can sever his foot in order to free himself from the chain and retrieve the gun with which he can shoot Adam.) There are all sorts of red herrings and twists to the complicated plot, as well as plenty of “gotcha” moments–both real and imagined–and episodes of stomach-churning violence (the titular instrument, you may be sure, does not go unused). And the whole thing is suffused with a grim, gritty atmosphere that emulates that of “Se7en” on an infinitesimal fraction of that picture’s budget.

By any objective standard “Saw” is pretty awful. The script is just a succession of tricks and sleights of hand, using brutal surprises and bouts of hysterical melodrama to distract viewers from the revelations that might lead them to guess the identity of the villain. (And when that final secret is disclosed, it goes way beyond implausible.) The acting is terrible across the board, with established performers like Elwes, Glover and Potter coming off worst simply because one expects more of them, even though the amateurish Whannell is completely out of his depth. (In fairness, he does manage a reasonably convincing American accent.) James Wan directs without the slightest trace of subtlety, ramming home every point with abandon and working with cinematographer David A. Armstrong and editor Kevin Greutert to maintain a dingy, depressing mood of foreboding punctuated by frenetic bursts of blood and innumerable verbal rants, as well as whiplash montages of images barely perceptible to the eye. (Of course, the flashbacks showing the killer’s earlier crimes are especially cringe-inducing: it’s hard not to be troubled by the sight of a woman trapped in an iron mask that threatens to rip her face apart, or a man encased in barbed wire.)

Still, for all its obvious ineptitude in plotting and production, “Saw” does what it sets out to do as a crude but effective exercise in cinematic manipulation. Though it will probably be compared most often (as above) to pictures like “The Usual Suspects” and “Se7en,” it’s actually more like the early movies of Wes Craven or even Abel Ferrara–messy and rather revolting, but carrying an undeniable visceral impact. On that level, “Saw” works. It just happens to be a very low level.