By Lionel Shriver

Farrar Straus Giroux. 427 pp. $22.95

"I've had it with goodies and baddies," says Estrin Lancaster, the protagonist of Lionel Shriver's new novel. "I'm more fascinated by bungling and murk."

Murk and bungling are exactly what Estrin finds in this shrewdly caustic and unexpectedly moving novel set in Northern Ireland in 1988.

Shriver's earlier fiction -- "The Female of the Species" and "Checker and the Derailleurs" -- has ranged in setting from Kenya to New York. Now she's added Belfast, where she currently lives. Shriver appears to have taken to her new home with a vengeance. "The Bleeding Heart" spares no one, offers no hope and -- here's the kicker -- is bitingly funny.

Estrin is a 32-year-old Philadelphia-born American who has drifted from trouble spot to trouble spot -- the Philippines, Israel, Berlin -- over the past 10 years. In each place, she quickly finds a job and lover, only to abandon them when they grow too constrictive or familiar.

Hers is a low-budget, downwardly mobile worldliness. Her marathon escape from privileged security has, until now, invigorated her. The only difference between her life and a foreign correspondent's, she says, is that she doesn't write it down.

But she's getting tired. As "The Bleeding Heart" opens, she's tending bar in a Catholic workingman's club in West Belfast and falling into a familiar pattern: grudging acceptance by the locals and uncertain romance with the most troubled, charismatic character in the place, Farrell O'Phelan.

O'Phelan is a marvelous creation: a former drunkard who turned his back on family and friends to become a nonpartisan freelance bomb disposer of legendary proportions. By the time he meets Estrin, he has given up bomb disposal for behind-the-scenes politics. An upcoming border poll on the unification of Ireland and a cross-sectarian conference designed to bring Protestant and Catholic factions together are consuming all his energies.

This makes him sound like a saint, and he's not. Instead, he's a ghastly-thin, six-foot-tall insomniac manipulator who derives a peculiarly masochistic pleasure from his exhaustingly frantic political maneuvers. When he's not politicking, he voices wry regrets that he didn't invest in pane glass and funeral flowers in 1968, before the lethal, window-shattering troubles began: "I'd be a rich man."

He's drawn to Estrin -- and contemptuous of her -- because she's a "conflict groupie," feeding off of social violence, just as he does. Both have uneasy love-hate relationships with their respective countries. Estrin sees being an American as "like any handicap -- harelip, paraplegia." Americans, she thinks, suffer from "mental incontinence," making no distinction between what comes into their heads and what comes out. But she gets impatient with outsiders' glib accusations about crass materialism: "Give us a little spiritual credit -- I've never met a single American who claimed if he could only upgrade to a multisystem VCR he'd be happy." When asked to guess whether Farrell likes being Irish, she tells him he abhors it, then adds: "In short, Ireland suits you perfectly."

That's the sort of paradox that's present on every page of "The Bleeding Heart." Catholic poets have clandestine affairs with Protestant politicians. Television reports on imminent factional reconciliation produce jubilant protests: buses set on fire, barricades. Terrorist groups admit to feeling they have to meet a reasonable monthly quota of bombings just for things to feel normal. Wheelers and dealers, outspoken sentimentalists, dreamers and hoodlums all hope to profit from the violence; would, in fact, be lost (as Farrell and Estrin might be) without it.

On every page, Shriver investigates the meaning of "normalcy" in a belligerent society and questions the healthiness of a camaraderie that comes from living under chronic crisis conditions. Belfast's atmosphere of random violence is often portrayed as partylike. When the party gets out of control, in the last 40 pages, Shriver yanks the cool protective rug of cynicism from underneath her readers' feet and lets them free fall. This is a challenging, disturbing fiction.

There are a few stumbling blocks for the general reader. Shriver is a profoundly gifted mimic. Born in North Carolina, she's gobbled Northern Ireland down and re-created it on the page with deceptive ease. At times, the book reads as if it were written exclusively for her Belfast co-residents.

There's a "Glossary of Troublesome Terms" -- not just a vocabulary list, but a scathing and incisive 12-page essay on Northern Ireland's political woes since 1969 -- which won't help you with words like "meal-a-crushie" or "banjax" or "glype." The book's initial scenes can be confusing as numerous characters are introduced. And, just before all hell breaks loose in the final chapters, there are passages of "helicopter thinking" (leapfrogging from one character's interior thoughts to another's) that simply don't move fast enough.

When you're into the wild swing of the novel, however, these become minor drawbacks. The bracing, acid wit and rich hyperbole are constant and a little terrifying. Who can be this cynical about horrors?

Shriver can -- and for a purpose. You may think she's numbing you with her wisecracking nightmare, when actually she's leaving you all the more vulnerable to her final devastating plot twist.

That's the ultimate paradox in this feverish book. "The Bleeding Heart" quivers with enticing energy, seduces you with its nervy amoral appeal.

The reviewer is the author of "Air" and "The Flame Forest."