By Peter Spiegelman

Knopf. 337 pp. $22.95

John March, the disaffected cop turned private eye who is the hero of this mordant, action-packed, knowledge-filled novel, lives in New York and minds his own business. He runs several miles every day, restricts his drinking to cranberry juice and club soda, and manages a meaningless if athletic sex life with his girlfriend, Jane Lu. A few years before, when March was still a policeman, his wife was murdered, and he drowned out his grief with sex, booze and violence. All that repels him now. But he is equally repelled by the bastion of phony respectability that his extended family represents. "Money is the family business," March remarks, "and it has been ever since my great-grandfather founded the merchant bank of Klein & Sons." Squadrons of his uncles, cousins and siblings are still affiliated with the outfit, and almost without exception they take a dim view of what March has chosen to do with his life.

Whatever his opinions about the world of finance, March has a very good idea of how it works. He spent his young adulthood interning on the floor of a big brokerage firm. "The avarice, egotism, and self-delusion I'd seen there approached caricature," he says, "and when the dismay wore off, Wall Street had bored me to tears." This knowledge comes in handy when Nina Sachs, a highly disagreeable artist who lives in a fashionable Brooklyn loft with Ines Icasa, a fetching Latina lesbian, hires him to track down her missing ex-husband, Gregory Danes. He used to be quite the financial celebrity on television talk shows until accusations of chicanery brought on the possibility of an investigation by the feds. It's not that Nina misses Danes in any way, she says more than once; it's that he's her main source of income. She needs the child support for their son, Billy, a troubled but brilliant 12-year-old who's coping as best he can with the divorce and his mom's new relationship, but the best he can do is not very much. He's plainly miserable -- and worried about his dad.

March is happy to take on the job. He's at home in a world where financial shenanigans are the norm, where the people he interviews threaten to sic their attorneys on him right after they say hello. When he visits Danes's investment-banking firm, he finds an office filled with dithering hysterics, none of them sure what happened, all of them fearing the worst. Is Danes dead? Or has he gone into hiding? If so, why? But they seem afraid only for themselves; none of them cares about Danes, whom they couldn't stand.

March discovers that Danes's life is -- or was -- extremely isolated and sad. He and March actually have a lot in common, including problems with relatives. While March's kin are lodged securely in the upper crust, Danes has a pitiful half-brother who resides in New Jersey, cold-calling potential suckers from a wretched boiler room, trying to sell them worthless stocks. Danes has dumped him as an impediment to his own supposedly safe and successful life. March knows all too well what that implicit disrespect is like; when he visits his brother's lavish apartment to celebrate his nephew's birthday, he has to keep from grinding his teeth. In all the clusters of framed family photographs that litter the place, there's only one of him -- taken when he was a very little boy. His family is embarrassed by him, the way Danes was ashamed of his brother.

What makes March such a willful misfit? He just doesn't want to play the game. He loathes all the give-and-take and inconvenience and compromise of daily life. He's not fond of humans. His girlfriend is as wrapped up in her work as he is. And his own work is lonelier than it might first seem: He gets much of his information from the Internet or the phone. His interviews usually end up in fisticuffs or a barrage of insults. He is desperately antisocial.

And so was Danes. Thus when March breaks into Danes's sterile, unwelcoming apartment, the detective feels a creepy shock of recognition. Danes's only apparent solace was his vast, obsessively categorized collection of CDs. In later talks with young Billy, March sees that he has his own collection of arcane comic books, which March, disconcertingly, knows almost everything about. The three guys are odd males out, weird birds, not at home in the world of human discourse.

March's search for Danes takes the reader on a tour of the American financial world. His interviews with people who might know something about the case reveal a television talk show hostess in bed (literally) with stock analysts who tout their own clients for gain. We see Danes's jackal of a boss, who has been hired by his firm to make out-of-court settlements with a slew of disgruntled clients to avoid further federal investigations. We see a hard-working woman who has given up her youth and any chance for a family because of the demands of her 16-hour workdays. It's a depressing picture, to put it mildly.

Others are looking for Danes, too, of course. Whoever they are, they're pretty tough customers. Soon, March is being threatened and followed. In fact, almost everyone in the novel is being threatened and followed. (The author perfectly captures the paranoia that comes from this phenomenon.)

Despite its generic title, "Death's Little Helpers" breaks new ground in detective fiction. What makes this novel original is its center in the world of big money. Sure, great wealth is alluded to in other noir novels, but at a far remove. The Maltese Falcon is forever out of reach, for instance, and Gen. Sternwood's millions (in "The Big Sleep") are perceived only in terms of his rotting oil fields and rotten daughters. Here, the wealth is taken for granted, but it's as bad for the characters as fried food. Peter Spiegelman worked more than 20 years "with leading financial institutions in major markets around the globe." That's how he learned about money. It doesn't say anywhere how he learned to write such a bang-up novel.