ALICE IN LA-LA LAND By Robert Campbell Poseidon. 269 pp. $16.95

"In La-La Land We Trust," Robert Campbell's first novel featuring the sometime private eye Whistler, was one of 1986's more riveting mysteries, opening with a scene guaranteed to get the attention of even the most jaded reader -- two hoodlums played soccer with a severed human head, while a horrified couple watched from an automobile, praying they would not be seen.

There aren't any moments quite as gruesome in "Alice in La-La Land," Campbell's follow-up, but it's an intriguing portrait of Los Angeles high life and low life, from the street people of the decayed Hollywood to the glamorous stars of Beverly Hills. Campbell's descriptions and dialogue snap and crackle; he can give a character's past, present and future in less than a paragraph. And when the writing is good, his words come at you like a tap on the shoulder in an unfriendly bar.

This time the down-on-his-luck Whistler (whose office is a booth in the window of an all-night coffee shop), takes a job as live-in bodyguard for Nell Twelvetrees, wife of top-rated television talk show host Roger Twelvetrees. Nell is divorcing Roger and fears he may decide to have her killed rather than pay a multimillion-dollar settlement. That night, someone breaks in and drugs Nell's dogs. Hearing her scream, Whistler runs to her rescue and is photographed embracing her.

From there on, the plot becomes increasingly tangled. Characters' paths cross and recross and cross again. (Among the most important are Spinneran, a blackmailer and sometime hit man, and Jenny, Twelvetrees' daughter, 21 and aching to experience life.) And just as the photograph of Whistler and Nell only seems to show them in a compromising position, most people and things in this novel are different from the way they initially appear.

Roger Twelvetrees, a man with a face like a "worried farmer, weary traveling salesman, small-town doctor cooling out after being dragged out of bed at three in the morning to birth a child or close the eyes of an old man just dead," is really a closet sadist with a penchant for beating young girls. Nell Twelvetrees is a former call girl. And Spinneran, who takes the photograph of Nell and Whistler, does it not for blackmail, but to get closer to Twelvetrees to exact his own revenge.

In this tangled skein, everyone is using everyone else -- except Whistler, who manages to maintain, if not his innocence, then a certain naive longing for miracles. He is a different kind of private eye, the cynical moralist, and those looking for a rock-'em-sock-'em ending will find the whole of this convoluted plot less than the sum of its parts. The detective in the mystery genre usually brings order out of chaos -- a crime has been committed, normalcy has been breached, and by uncovering evidence and apprehending the criminal, the detective makes the world safe again. Whistler is more of a witness than an actor in the drama, and his authority stems not so much from his power to set things right as from his moral force. He lives by a code, albeit one that is no better articulated than "When you got older, you got wiser, and you went home early to get your sleep."

We'd like, I think, to know a little more about him than the melancholy fact that as he escorts Nell to his car, he remembers "a night when he'd worn a white dinner jacket." Or that at one time, about 15 years earlier when "he'd been just about ready to eat the world," he had loved a would-be actress named Connie Ranger. Whistler has been around and he knows Hollywood; what's not clear is why he came and why he stays.

But quibbles aside, Campbell excels in his portraits of minor characters and in building a believable world. It's all there, from the studio commissary where Twelvetrees bullies an autograph seeker, then humiliates a waitress in front of his fawning aides, to the two-room office of Philly (The Fink) Torino and Mocky Hush, proprietors of a security agency that "provided rent-a-cops for parties, retail sales, and the openings of gasoline stations and headshops" and "arranged contract murder for respectable citizens tired of wife, husband, boss, or lover."

The reviewer is an assistant editor of Book World.