BOOK REVIEW : The Walking Wounded and the Satanists in La-La Land : THE WIZARD OF LA-LA LAND <i> by Robert Campbell</i> , Pocket Books $20, 306 pages

Two rules of genre fiction:

1) All surprises have to come from the plot. The reader doesn’t want to be surprised by the atmosphere, the characters or the world-view implicit in the story, much less by the author’s technique. (Imagine, Vladimir Nabokov once proposed in mock horror, a mystery without a word of dialogue, in which “the real crime is artistic originality.”) All these are supposed to be cozily familiar.

This is why genre writers such as Robert Campbell are often better plotters than their mainstream colleagues: They have no choice.

2) The Bad Thing that provides the thrills and chills in a genre story--whether it’s dinosaurs or Klingons, outlaws or international spies, vampires or rabid St. Bernards--is usually just a stand-in for what really frightens us: a dramatic shorthand for life’s grayer, more nebulous terrors.

The Bad Thing in “The Wizard of La-La Land,” the fourth novel in Campbell’s series about a Hollywood private eye named Whistler, is satanists.

They are nasty folks indeed. A clique of the untouchably rich, they have youngsters kidnaped from Mexico to satisfy their perverted lusts; they hold orgies in a Malibu hideaway at which children are ritually butchered.

One such victim, years ago, was Sarah Canaan, niece of Los Angeles Police Department Sgt. Isaac Canaan. Her murder was never solved, but Kenny Gotch, a male prostitute dying of AIDS, mentions something about it to a relative, who consults Mike Rialto, a cardsharp and pimp who knows Canaan and Whistler.

Rialto, by the standards of Campbell’s universe, is a good guy. He agrees, however reluctantly, to see Gotch--only to find him dead in a hospice, and not of AIDS; his throat has been cut with a tiny surgeon’s knife.

Since this is a hard-boiled story more than a whodunit, we learn early on who killed Gotch. Deftly, Campbell introduces a slew of other characters whose relation to either crime is unclear. They include a one-armed coffee-shop philosopher, a bereaved mother, a priest, a UCLA professor, a hooker who moonlights as a hospice candy-striper, a nurse who doubles as a practicing witch and an evil mastermind who is crumbling into senility.

Much of the suspense comes from wondering how all these people fit together. The rest comes from wondering how the good guys can possibly win. Campbell’s heroes, true to the genre, are walking wounded, decent but deeply cynical, negotiating a Hollywood of smoggy skies and tarnished dreams. Above all, they are crippled by guilt--whereas the bad guys are cunning, powerful and sublimely guiltless.

Whistler goes to work. His clues: the 24 speed-dial numbers on Gotch’s telephone and the mummified finger of a child, probably Sarah Canaan.

Meanwhile, Campbell (who also writes the Jimmy Flannery and Jake Hatch series) feeds us inside information. In case you ever wondered, a “twangy boy” is a male hustler who claims not to be gay. And at the UCLA Medical School, fresh cadavers for anatomy classes are “stacked up on overhead conveyors . . . modified ice tongs in their ear holes.”

This adds to the coziness that helps us stomach all the seamy stuff. So does our confidence that Campbell’s puzzle pieces will fit. And so does the sense that this novel is connected to the rest of the “La-La Land” series, even if, viewed alone, it’s oddly shaped.

The beginning--Sarah’s murder--is summarized quickly, as if it’s something we already know. The ending is garish but equally quick. “Wizard” is almost all middle: details of detective work, social commentary, occult lore, a bit of romance. Characters from previous books loom larger than this story strictly warrants--a flaw, perhaps, but a reassuring one.

Genre readers need all the reassurance they can get. Only then can they allow themselves to be scared by a surrogate for what actually worries them--and then leave the fear behind when they close the book. Satanic cults exist, of course, but in today’s America, corporate downsizing causes more pain and anguish than devil worshipers, Mafia hit men and terrorists combined; it just doesn’t make as nifty a story.