Of his on-going franchises - the not terribly interesting railroad detective Jake Hatch; the light and likeable Chicago-based Jimmy Flannery stories - praise be that Robert Campbell's new novel goes back to Whistler. Along with his brilliant one-off Juice, Campbell's La-La Land trilogy - In La-La Land We Trust, Alice in La-La Land, Sweet La-La Land - are his finest published work. These are the trials and tribulations of the ageing private eye down among the pushers, pimps, whores, baby hookers and twangy boys running like sewer rats through the slightly mythical, slightly surreal gutters beneath the Hollywood sign.

Well, finally three becomes four with this all new, seemingly end-tidying book. A young twangy boy - Kenny - does a lonely death on an AIDS ward, taking with him the name of the man sought for the last decade for the vicious murder-mutilation of a young girl. But Kenny's slow, agonising death was helped along by a small surgical blade puncturing his throat. And why was he studying Occult texts in his squalid little apartment? Nor was the girl just any victim: her uncle - Isaac Canaan - is the most dedicated vice man on the force, sworn never to rest until his niece's killer sees justice. Canaan's friend Whistler is soon involved and a chase is met through the murky world of Satanism, paedophilia and South American child stealing gangs.

First things first - The Wizard of La-La Land is missing something. These slightly retro, noir-washed streets seem underweight, and often there are too many characters peopling these pages. The nurse Mary Bucket, a woman whose child was snatched in South America, street boy Pooch, a flame-haired professor, the psychopathic Rehab; and all on top of the usual La-La Land suspects like Canaan and Bosco, the cafe-owning, one-armed intellectual. After a strong start - the reviving of the old mystery of the dead girl, the almost missed murder, the grace under pressure of photographer-cum-assassin Rehab - Campbell loses the thread and allows the book to spiral in a confusion of subplots in a most irritatingly discordant muddle. The path leading to child stealing promises but gets lost in amongst everything else. Another La-La Land novel might so easily have started here.

Better is all the Satanic stuff. Campbell gets down to it in a confusion of occult strands and twisted motives. White witches bump spells with ancient magics, Satanists veer between highflown magick and the more pragmatic needs of a Halloween show for the exclusive clientele of a club called Lucifer's. That last - with hookers hired for the show complaining about the cold and arguing who gets to play the naked altar this year - is a glimpse of the tongue in cheek nastiness that makes the other books so cherishable. But that gives out to a rushed, garbled climax that ill-serves a writer as good as this.

While never actively bad, The Wizard of La-La Land is a disappointment, especially coming relatively recently after the equally disappointing Boneyards. Robert Campbell now seems so comfortable in the warm, endearing, swiftly wrapped mysteries in the world of Jimmy Flannery that the heart has gone out of his better, more vicious writing. Here's hoping.