By Steve Martini

Putnam. 402 pp. $25.95

The leading writers of legal thrillers distinguish themselves in various ways. Scott Turow is known for the depth of his characterizations. John Lescroart offers a rich portrait of the San Francisco legal world. Robert Tanenbaum and Stephen Horn share an insider's understanding of how Washington works. Steve Martini, on the evidence of this, his 10th novel, has an unsurpassed understanding of just how cynical, not to say sleazy, the legal world can be, and we are talking here about the lawyers as well as their clients.

His man Paul Madriani, whom Martini has chronicled in previous novels, is no sleaze; he won't take drug cases and, in the context of this novel, he is a saint. But he has a friend named Nick Rush who is a piece of work: a chain-smoking, fast-talking million-dollar-a-year defense lawyer who welcomes drug cases, mesmerizes juries and is trying to keep his 26-year-old trophy wife happy while conspiring to seize control of San Diego's biggest law firm.

At the outset, Rush asks a favor of Madriani. Rush's sexy young wife has a friend who needs a lawyer. Nothing serious, probably just needs to have his hand held. Madriani unwisely agrees to talk to the fellow, a contractor named Metz, who he learns has been involved in a murky deal in Mexico where $2 million changed hands. Madriani decides that Metz is probably guilty of any number of felonies and sends him back to Rush. A few days later, while standing in front of the federal courthouse, Rush and Metz are gunned down by drive-by shooters who escape without leaving a clue.

Poor Rush is barely in the ground when Madriani is summoned by his glamorous widow. It seems that her husband's law firm had a $2 million policy on him. The bad news is that his first wife is listed as its beneficiary. As Madriani unscrambles this problem, he meets the head of the firm, one Adam Tolt, who looks like "a cross between FDR and the devil." Indeed, the cunning Tolt is the most interesting character in the novel, for it is not at all clear whether he is a legal statesman or a very wicked man. Madriani and Tolt form an alliance; Madriani wants to know who killed his friend and Tolt wants to protect his firm from adverse publicity. They share an uneasy suspicion that the sexy widow might have had her husband killed.

Martini spices his story with pithy comments on politics and law. He scorns politicians who have "institutionalized the destruction of public ethics by elevating deceit to a statecraft called 'spin.' " He says most lawyers agree that "justice, if it exists at all, is a mere by-product of making money." An angry Tolt warns that if anyone accuses his law firm of illegality, "they're going to be looking at an action for business disparagement that will take their house, their dog, their wife and their retirement, not necessarily in that order." In one nice scene, wary lawyers gather to negotiate the insurance payout amid "much mutual sniffing."

All this is good fun, but about two-thirds of the way through the novel I realized I had no idea where the story was headed and, worse, I began to fear that the author didn't either. That's when the novel goes south (well, southeast), as Madriani and Tolt fly to Cancun to investigate the dead men's dealings there. Soon, instead of lawyers doing battle with their writs and wits, which Martini does well, we have two American lawyers in dubious battle with Mexican bandits. In one improbable scene, gunmen blast away at Madriani from an "ultralight" airplane circling above the pool of his luxury hotel. He meets an aging Mexican gangster who has been searching for years for a priceless Mayan artifact, the Mexican Rosetta Stone; this plot line, with its faint echo of "The Maltese Falcon," unfortunately goes nowhere. The merry widow appears briefly then is seen no more. Finally, Madriani plunges into the jungle and winds up in a climactic shootout atop a Mayan pyramid. Whereupon the reader must ask: What is a rational man like Paul Madriani, who has a much beloved 15-year-old daughter waiting at home in California, doing dodging bullets atop a pyramid?

In television they call this jumping the shark. When all else fails, create a diversion. Climb a pyramid. Dress in drag. Put on water skis and jump a shark. Maybe the poor befuddled reader will think it somehow all makes sense. It doesn't, but Martini is a crafty pro and if this tale misfires, no doubt he'll conjure a better one the next time out, preferably one that stays in California and focuses on good old American sleaze.