By Andrew Vachss

Knopf. 255 pp. $17.95

Of the current mystery writers advertised as hard-boiled, none is more ambitiously original -- and crazily uneven -- than Andrew Vachss, whose "Blossom" is the fifth novel featuring Burke, an ex-con and private investigator specializing in runaway teens and child abuse. Vachss is a real-life Manhattan attorney dealing regularly in these sorry matters, and his expertise shows in his horrifying sketches of kids corrupted and wounded, often beyond healing, by psycho- and sociopaths who often were similarly victimized as children.

For a writer who presents himself as a tough guy drawn to degradation, Vachss also comes up with some surprisingly gentle and nuanced portraits of adult women whom he clearly respects and enjoys. The title character of "Blossom" is a funny, sexy, self-possessed former-hillbilly MD who, discovering that Burke has brought no condoms for their sexual encounter, tells him, "Forget it. What year do you think this is? I didn't go to medical school to have some strange man playing with my life. I don't know where you've been." Abashed, Burke heads for the drugstore soon after this refreshing scene.

Where Vachss doesn't do so well in "Blossom" is in the plotting -- as rambling and episodic as real life, and about as suspenseful -- and in some of the writing, where Vachss comes across as an overripe Jack Webb. New York City is "a rancid underbelly turned on its back -- the maggots at home, not running from a sun that would never shine. A city of ambulatory psychopaths, choking on ethno-insanity." When a "freak" tells Burke he paid $25 for a misogynistic porno mag, Vachss writes, "In the underbelly of the human heart, dirt isn't cheap."

Burke customarily works in New York, where he makes a living, in the words of a cop friend, "working the edge of the line. Finding missing kids, stinging kiddie-porn dealers, roughing up pimps." In "Blossom" he is called away to the steel mill region of Gary, Ind., where Burke's former cellmate Virgil needs help. Virgil's nephew Lloyd stands accused of four lovers'-lane sniper murders. Burke's job is to find out if the kid, a chronic peeping tom, did it -- in which case Virgil may mete out justice himself -- or, if Lloyd is innocent, who the real killer is. Most of the local police "want to close cases, not solve them," but Burke finds a brainy, skeptical detective on the local force who feeds him enough information for him to do the cops' job for them.

What we have here basically is an unexceptional police procedural, except with the officials' work being performed by one of the stranger antiheroes in crime fiction today. Burke is an "ugly" man with "a convict's patience," a lover of lost just causes who once soldiered as a mercenary in Biafra, a man who uses "a Zen exercise" to solve crimes, and who can anticipate a "sex-sniper's" next move by "being him in my mind." Why Burke, who was convicted of hijacking, can "be" a sexual psychopath more effectively than others can "be" one remains murky.

When Vachss isn't writing badly, he often writes wonderfully, and it is these not-infrequent inspired passages that will carry a lot of readers along to the routine finish. All the scenes with Blossom are sweet and real, as are the ones with Virgil's wife, Rebecca, a woman whose "voice was hard coal, from a deep vein." The blue-collar urban-Appalachian men are affectionately drawn; Vachss can make people who love guns comprehensible. Here is Burke telling Lloyd what prison is like, in case he has to go: "Prison's not like jail. Prison, there's nobody coming to the gate with bail money. You're down for a long time. You count the days. Some guys, they got too much time to count for themselves, so they look to take a piece of yours. ... It's like the street, only ... compressed, you got it? Everything happens close up. There's no place to go. No place to hide. So you give nothing away. Nothing. Never. Look down or look hard. Your face stays flat. You don't smile, you don't cry. And you protect your space ... the space you carry around with you ... the space around your body."

The men in "Blossom" who talk about the harsh survival codes of prison life have other sides to them too, often brought out by women and by music. One night Burke, Blossom and Rebecca are in a Chicago blues club where Virgil, a gifted sometime musician, sits in with the band. "Virgil's piano was a magic thing -- sweet water flowing over crystal rocks, breaking and falling, spooling out a ribbon of purity across the bottom, climbing again. He and the fiddle player laid down a carpet of neon smoke, the slide guitar man lancing through, long fingers high up on the neck, counterpointing the harp, bending unreal notes between them like playing jump rope with metallic strands. The steel guitar cried to itself." Lovely.

Vachss does some nice quick sketches of minor characters too. A self-important U.S. senator almost caught in a sex scandal "wasn't cut out for crime. He was the kind of man who'd use vanity plates on a getaway car." An assistant district attorney Burke meets is "the kind of guy who screws something up so many times they call him experienced."

Even with the slow plot and redundant underbellies, "Blossom" is a fascinating piece of crime fiction noir.

The reviewer is the author of three mystery novels published under the pseudonym Richard Stevenson.