The Spanish Prisoner is Mamet's latest hand of cinematic three-card monte, a brazenly contrived and sneakily entertaining thriller that has no higher purpose than hoodwinking the audience. The mark is Joe Ross (Campbell Scott), an uptight Boy Scout of a corporate underling. Along with his loyal partner (played by Mamet regular Ricky Jay, in real life a magician and bunco historian), Joe has worked out a top-secret market-controlling formula called "The Process."

We never find out exactly what "The Process" is or does; the generic name is Mamet's tongue-in-cheek acknowledgment of its function to the plot. (It might've been called "The McGuffin.") All we need to know is that Joe's formula can make somebody vast amounts of money--and that someone is scheming to take it away from him. As a sinister plot takes shape against Joe, the suspects include Joe's demanding boss (Ben Gazzara), some creepy lawyers, and a shady dealmaker named Jimmy (Steve Martin). But who--and how?

The "who" is obvious early on; the "how" is the fun part, meticulously devised by Mamet in a long windup of red herrings and planted clues. The Spanish Prisoner is a variation on Mamet's experimental "radio play" The Water Engine, in which a naive inventor is swindled and crushed by unscrupulous moneymen; the dialogue has the same retro melodramatic feel, punched up with the loungy menace of Carter Burwell's score. Even without Mamet's trademark profane sparring, the language is spiky and surgically precise--so much so that the merest confusion over the meaning of the words "dropped off" triggers severe repercussions. At worst, Mamet's writing here settles into Joe Friday copspeak; at best, he fills us with dread about how much of ourselves we give away with just the simplest word choice.

The cast has a blast swatting Mamet's curveball lines back and forth. Campbell Scott, who always seems slightly uncomfortable in his skin, is astutely cast as Joe, whose streak of resentment and distrust makes him a perfect patsy. Among a small army of expert sharpies, the surprise standout is Steve Martin, whose shivery elegance is smashingly effective. Something about the expert way Martin wears an expensive suit--as if it were peacock's plumage, camouflage, and body armor all at once--is enough to convince us Joe's in way over his head.

The one weak link is Rebecca Pidgeon as a ditzy receptionist, but the writer/director deserves equal blame. He gives her the movie's worst lines--the ones that sound like Mamet parodies, with repeated, rephrased, accusing statements punctuated by somebody's name--and then coaxes from her the sort of stilted, hypnotized line readings he demanded from Lindsay Crouse in House of Games. The gimmick doesn't work the second time around.

As much as he may aspire to be a grifter, though, Mamet's real gift is for the humiliation suckers feel when they've been fleeced. Con games are psychology, and the hurt doesn't come so much from being easily duped as from being easily read. Who wants to feel he can be sized up at a glance--that his weaknesses are that close to the surface? Joe gets royally rooked, and we get taken right along with him because Mamet knows exactly how to misdirect our attention, even when we think our eyes are wide open--especially when we think our eyes are wide open. Even if The Spanish Prisoner isn't quite in the same league with his previous hustles, House of Games and the criminally underrated Homicide, it's worth a second look just to see how clearly David Mamet has us pegged.