What happens when a girl of the Paris Hilton ilk (though, in this case, not dumber than a loaf of pumpernickel) becomes the target of a sophisticated coterie of assassins? As one might expect of a spoiled rich girl for whom everything has come too easily, she gets lucky. She gets Joe Pike for a bodyguard in “The Watchman” (Simon & Schuster, 292 pages, $25.95), the new thriller by Robert Crais.

Mr. Crais, one of the most consistently excellent mystery writers working today, usually writes about Elvis Cole, who, with the possible exception of Robert B. Parker’s Spenser, is the funniest wise-cracking private eye in the world.

Cole’s enthusiastic fearlessness often lures him into situations in which he needs a hand, which comes in the form of Joe Pike, who thinks anything beyond a monosyllable is unbearably loquacious and who smiles as often as someone walking up the steps of the gallows. He is also a killing machine who must exercise all his skills to keep his young charge alive.

Larkin Conner Barkley stupidly roars through the streets of latenight Los Angeles, inevitably crashing into another car. The man and woman in the front seat speed away while their back-seat passenger runs in the opposite direction. Because Larkin has seen these people, teams of professional killers attempt to permanently shut her up. Her wealthy father hires a high-priced security firm to protect her. The head of the firm, a former L.A.P.D. officer, believes that the only person he can trust with the assignment is the man he trained years before. Pike is forced to take the job as payment for a debt he owes his old partner.

Moving from one safe house to another, Pike and the girl find assassins waiting for them, so the former Marine and mercenary drops out of sight with her, trusting no one except himself to protect her. Well, he trusts Elvis, too, of course, and his friend’s detective work helps determine how many killers are on the girl’s trail.

Suspicion is rampant because there can be no doubt that someone on the inside — the girl’s father and his lawyer, the security firm, the FBI — is providing information to a drug cartel and its hit men. A huge real estate deal, with more than $100 million at stake, can buy a lot of firepower, but following the money trail is no small feat.

Pike enlists a criminalist to provide some elusive information. John Chen is very tall, very skinny total geek who is terrified of Pike. Absolutely convinced that Pike will beat him to death if he doesn’t get him the answers he seeks, Chen proves a valuable ally when it seems that no member of the police force can be trusted.

As Pike and Larkin spend more time together, the ultimate odd couple — she wildly exhibitionistic, he attempting to be invisible — develop mutual respect and affection. He recognizes a kindred mentality. Because his father used to beat him when he was young, Pike tried to quietly disappear to avoid the brutality. Because her father ignored her, even speaking to her mainly through his lawyer, Larkin flaunted herself at every opportunity. They are alike, Pike decides, and he will do anything to keep her alive.

Civil libertarians might have a problem with Pike. He does not check to ask for ID, nor does he issue warnings. He doesn’t try to understand the problems of criminals, nor the childhoods that may have led them into a life of crime. Instead, he just shoots them.

When he learns that more than a dozen thugs are on their trail, he knows what to do. “All these bastards trying to kill this girl,” he muses, “this one girl, all of them ganged against her, and he would clear the field, but not for justice. It would be punishment. Punishment was justice.”

This isn’t taught at Harvard Law or any known police academy, but it proves to be a highly effective approach to law and order.

Mr. Crais, as he has proved in his earlier Elvis Cole novels, as well as such white-knuckle suspense tales as “Demolition Angel,” “Hostage,” and “The Two-Minute Rule,” has an extraordinary ability to mix blindingly fast action with sensitive character studies, violence with humor, and complex plots with stylish prose.

“The Watchman” provides the first-in-depth look at one of the toughest characters in contemporary crime fiction. Utterly autocratic, hypnotically focused, and eerily silent, Pike does not seem like a lot of fun. But reading about him is.