GOING WRONG By Ruth Rendell The Mysterious Press. 260 pp. $18.95

Among mystery readers, there are three main schools of thought on the prolific Ruth Rendell. Her most devoted fans -- and there are many tens of thousands of them -- find the British grande dame of psychological suspense almost as deep as Dante in her understanding of human folly and evil. The Rendellites love her gift for laying bare the eeriness in ordinary life, and for these readers Rendell's slower-than-usual pace is wonderful torture. Among those who don't go for Rendell at all, her minute probings of character fail to compensate for the too-straightforward plots that often feel like shaggy dog stories. Where's the mystery? these readers ask.

A third group -- which has a good time visiting Rendell's exquisitely drawn world of genteel rot but wishes she wouldn't dissipate the suspense so much by frequently revealing the killer's identity, a` la Columbo, in the first chapter -- might join the Rendell claque in its enthusiasm for her latest offering. In "Going Wrong," we're sure we know right away who is going to commit a ghastly murder; the question that keeps us happily mystified is who the victim will be. This old-fashioned sly stunt is one of Rendell's niftier performances.

Guy Curran, whose supple, disturbed mind is the focus of Rendell's scrutiny in "Going Wrong," is a suave young paranoiac who climbed out of the London slums dealing drugs. He "made a little fortune leading schoolchildren astray," and now, closing in on 30, Guy has gone pretty much straight: He owns a nightclub, a travel agency and a lucrative painting "factory," where art school peons knock out "original" works called "Man's Best Friend" and "Carry On, Kittens" by the hundreds. Guy has every thing he wants in life except one. Leonora Chisholm, while not of Guy's class, was briefly his teenage lover more than a decade earlier. Although she's moved on to a life among the "lefty, 'green' do-gooders," as Guy sees them, "who thought there was something morally proper about not having a freezer or a microwave," Guy is still obsessed with Leonora. He phones her daily and they have lunch every Saturday. Her family despises Guy, but Leonora can't quite let him go; to be desired so passionately is irresistible.

Leonora's acquiescence to his attentiveness fuels Guy's delusion that she will one day marry him -- he fantasizes about their cozy life attending family weddings and funerals -- and when Leonora becomes engaged to a BBC producer, Guy can only conclude that a member of her family or circle of friends has turned Leonora against him. It's the only possible explanation, since "a woman always loves her first best." To release Leonora from this fatal spell, the person who controls her mind must be identified and killed. Using his underworld contacts, Guy puts out a contract first on a relative, then a friend of Leonora's, then another relative, each time bumblingly canceling the previous contract.

Rendell is terrific at seeing the world through Guy's immense need. When Leonora holes up in her fiance's flat and refuses Guy's calls, Guy concludes that "Newton had unplugged his phone to make it impossible for Leonora to speak to him. Most likely, almost certainly, Leonora did not know this." After Leonora's engagement is announced, Guy tells her: "I suppose you had that rubbish put in the paper to please your family." When Leonora ends an exasperating phone conversation with "Oh, Guy, how I wish ... " he finishes her sentence in his mind: "How I wish we could be as we once were."

If Guy is frightening and pathetic, Leonora and her circle are in many ways scarier. Her mother, Tessa, is a caustically drawn caricature of middle-class intellectual pretension who scorns Guy, to his face, as "a common piece of rubbish from a council house." Her vilest epithet for Guy is not "gangster" but "Philistine!" In a rare moment of kindness, Tessa suggests Guy see a Jungian analyst she knows.

In the end, the most monstrous character -- a real doozy of passive-aggression -- turns out to be sweet, laconic Leonora. For 10 years she has been hounded by a lunatic, and when she insists she is going to marry another man, the lunatic shouts at her: "I am the love of your life and you know it. If you refuse me I'll stop you. I won't let you get married. I have a right to forbid your marriage and I will." Does Leonora flee? Phone the police? "Guy," she says, "sometimes you say things to me which make me seriously question your sanity. I mean that. And it's getting worse. I honestly think you need to do something about it." Says Guy, "You've been listening to your mother."

As is always the case with Rendell, the awful things that happen are less important in the narrative than the awful things that are constantly threatening to happen. Guy's indecision about whom to have "disappeared" borders on the farcical, like a Thomas Berger plot set in Holland Park instead of southern Ohio. One suspect is brushed by a speeding car and escapes with a mere concussion before Guy decides he's not the culprit who is poisoning Leonora's mind. A pal of Leonora's leaves for a holiday in Spain the day she's to be bumped off. And on, and on. It is only after Guy is finally -- quite believably -- free of his obsession that farce turns to double tragedy in this leisurely, masterly dissection of deluded souls.

The reviewer is the author of three mystery novels published under the pseudonym Richard Stevenson.