By Karin Slaughter. Morrow. 360 pp. $24.95 You get a lot of bangs for your bucks in Karin Slaughter's new thriller. Fourteen pages into Indelible, pediatrician Sara Linton and others are taken hostage in the Grant County, Ga., police station, which two gun-wielding intruders have strewn with gore and dead bodies. Just as that imbroglio is raising hairs, Slaughter launches a subplot that occurred a decade earlier, at the beginning of the love affair between Sara and her ex-husband, Jeffrey Tolliver, who is now Grant County's police chief and one of Sara's fellow hostages. Soon this flashback, set in the Alabama town where Jeffrey grew up, turns tense, too: Sara and Jeffrey arrive at the house of his best friend, Robert, shortly after Robert has apparently shot an intruder dead and taken a bullet in the abdomen. From that point on, the narrative switches back and forth from the hostage scene to the investigation of the double shooting, which looks a bit fishy to Sara's medically trained eye.

On top of all this, Indelible is a prequel, designed in part to fill in the backgrounds of Sara and Jeffrey, who recur in other Slaughter novels. The question is whether the author does justice to the multiple layers of her material.

Almost from the start, I found the flashback the more interesting of the two storylines. Mayhem in a police station, followed by a hostage-taking, may be ideal thriller fare, but one of Slaughter's strengths is her charting of post-sexual-revolution male-female dynamics, and this comes to the fore in the earlier, Alabama sequences. At that stage, Sara and Jeffrey have slept together several times but still hardly know each other, and much of what his friends say about him comes as news to her -- that he went to college, for example. What she does know is that he deserves the nickname his pals greet him with -- Slick -- so much so that she's of two minds about his riposte to her observation that a handsome, randy guy like him must have "screwed practically every woman in town": "They were just place-holders while I waited for you," he says. It's a perfect line, especially when delivered by a man who acts on Sara "like some drug that she could not get enough of," and she wants very much to believe him. But he's not Slick for nothing, is he?

Their process of getting acquainted becomes even more fraught when Sara and Jeffrey duck into a local cave to escape a rainstorm and discover a human skeleton inside, its skull bashed in such a way as to indicate homicide. Turns out that Jeffrey's old friends -- some of whom are policemen, too -- figure in both cases: the double shooting and the remains in the cave. Just how they are implicated lies at the heart of the mystery that unfolds as the young lovers keep sparring and sizing each other up.

For that matter, the novel's two main foci -- past murders and present-day hostage crisis -- are not as discrete as they first appear. The main thread tying them together is all the sleeping around engaged in by the younger generation of Alabama townspeople. (The not-so-subliminal message is that sex is apt to be more powerful -- and have more lasting effects -- than bed-hopping teenagers would like to believe.)

Throughout Indelible, Slaughter excels at pitting one strong character against another. A long conversation between Sara and her mother, as Sara gets ready to go off for a weekend with Jeffrey and her mother takes over the packing, epitomizes the blend of love, bossiness, resistance, banter and tenuous compromise that shapes relations between a tough-minded parent and a willful child. And in Slaughter's steady hands, the trajectory of Sara and Jeffrey's off-and-on romance is clear and convincing.

Ultimately, though, too much happens in this book. For all its deaths and splattered walls and countdowns toward the moment when the cops will rush their own station house, the hostage crisis gets shortchanged. Maybe Slaughter asked too much of herself in trying to fuse a prequel with an update (the outcome of the present-day crisis sets the stage for a new act in the Sara-Jeffrey relationship). To readers who concentrate on the Alabama murder case, however, Indelible will give considerable pleasure. *

Dennis Drabelle is a contributing editor, and the mysteries editor, of Book World.